Blood pumps

ABSTRACT

A blood flow assist system can include an impeller assembly including an impeller shaft and an impeller on the impeller shaft, a primary flow pathway disposed along an exterior surface of the impeller. The system can include a rotor assembly at a proximal portion of the impeller shaft. A secondary flow pathway can be disposed along a lumen of the impeller shaft. During operation of the blood flow assist system, blood can be pumped proximally along the primary flow pathway and the secondary flow pathway. The system can include a sleeve bearing distal the impeller. The system can include a drive unit having a distal end disposed distal a proximal end of the second impeller. The drive unit comprising a drive magnet and a drive bearing between the drive magnet and the impeller assembly.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application claims priority to International Application No.PCT/US2020/062928, filed Dec. 2, 2020, which claims priority to U.S.Provisional Patent Application No. 62/943,062, filed on Dec. 3, 2019,and to U.S. Provisional Patent Application No. 62/947,940, filed on Dec.13, 2019, the entire contents of each of which are hereby incorporatedby reference herein in their entirety and for all purposes. Any and allapplications for which a foreign or domestic priority claim isidentified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 C.F.R. § 1.57.

BACKGROUND Field

This invention relates to improved blood pumps.

Description of the Related Art

In the field of cardiac assist devices and mechanical circulatorysupport, blood pumps are used to support the heart in circulating bloodthrough the body. Implantable impeller pumps make up one common class ofblood pumps used.

Impeller pumps use bearings to connect the impeller to the rest of thepump in a way that constrains the impeller both radially and axially,but leaves it free to rotate. Sleeve bearings (or journal bearings) area common type of bearing that provide radial confinement. Cone bearingsprovide both axial and radial confinement. Both sleeve and cone bearingsalso have improved pressure-velocity characteristics (due to theirtwo-dimensional bearing interfaces), in contrast to bearings that relyon point or line contact.

Blood pumps also typically include structure that provides torquecoupling between the motor and the pump impeller. Common variations ofthis design element are direct torque coupling and magnetic torquecoupling.

SUMMARY

There remains a continuing need for improved blood pumps.

One major difficulty with blood pumps is sensitivity of blood to theconditions created by the pump. Common problems include blood clots andhemolysis, especially with bearings that have areas where blood canstagnate and clot.

Key factors in the design and evaluation of blood pump comprise:enhancing fluid flow to the bearing regions, enhancing fluid flow fromthe bearing regions, creating lubricating fluid layers in the bearingregions, maintaining the pressure-volume characteristics of the bearinginterfaces within favorable ranges, and minimizing forces on the bloodthat can lead to thrombosis or hemolysis.

In one embodiment, a modular bearing system for blood pumps is providedthat enables different combinations of bearing design elements withunique and novel advantages. A first bearing is a sleeve bearing (orequivalently, a journal bearing) uniquely designed to allow flow throughthe pump with minimal obstruction. The other is a cone bearing. In someembodiments, one or more of these bearing designs may be used. In otherembodiments, either bearing design may be used with additional bearingdesign(s). In other embodiments, the two bearing designs may be usedtogether in a configuration that provides additional benefits.

The sleeve bearing may have a modified geometry for reduced thrombosis.Various low thrombosis sleeve geometries are considered. The sleevebearings may contain added features (e.g. a thrust ring) that providesome degree of axial confinement as well as radial confinement.

The cone bearings described in this disclosure have modified geometriesthat promote full washing of the bearing surfaces by blood. The fullwashing of the bearing surfaces may be promoted by enhanced sourcing ofblood to the bearing region, enhanced removal of blood from the bearingregion, or some combination of these.

The sleeve bearing and the cone bearing may have certain features thatsupport their combined use and offer unique advantages arising fromthese combinations.

In several embodiments, a blood flow assist system is disclosed. In someembodiments, the system consists essentially of an impeller assemblycomprising a rotor assembly and an impeller coupled with the rotorassembly, the rotor assembly comprising a first curved bearing surface(e.g., a concave bearing surface), and a drive unit proximal theimpeller assembly, the drive unit comprising a drive magnet and a drivebearing between the drive magnet and the impeller assembly, the drivebearing comprising a second curved bearing surface (e.g., a convexbearing surface) shaped to mate with (e.g., fit within) the first curvedbearing surface. In some embodiments, the first curved bearing surfaceincludes a fluid port. In some embodiments, the second bearing surfaceincludes a void (e.g., a central hollow) and one or more channelsextending radially outward from the void. The void can be in fluidcommunication with the fluid port so as to direct blood radially outwardalong the at least one channel. In some embodiments, the convex bearingsurface has a distal end disposed distal of a proximal end of the rotorassembly. In some embodiments, the convex bearing surface comprises aplurality of distally-projecting segments, the plurality ofdistally-projecting segments spaced apart circumferentially to define atleast one channel between adjacent segments.

In various illustrated embodiments, the rotor assembly can include aconcave bearing surface, and the drive bearing can comprise a convexbearing surface. However, it should be appreciated that, in each of theembodiments disclosed herein, the rotor assembly may alternativelyinclude a convex bearing surface and the drive bearing can comprise aconcave bearing surface, with the convex bearing surface mating with(e.g., fitting within) the concave bearing surface. Further, inembodiments in which the rotor assembly comprises the convex bearingsurface, the plurality of segments may extend proximally (e.g., asopposed to distally-extending) and can be spaced apart circumferentiallyto define at least one channel between adjacent segments.

In some embodiments, the rotor assembly comprises an impeller shaft anda rotor magnet coupled to the impeller shaft, the impeller disposed onthe impeller shaft. In some embodiments, the impeller assembly comprisesa second impeller disposed on the impeller shaft spaced apart proximallyfrom the impeller along the impeller shaft. A flange can extendnon-parallel from a proximal end portion of the impeller shaft, thesecond impeller comprising a plurality of vanes disposed on a generallyproximally-facing surface of the flange.

In some embodiments, the impeller is configured to pump blood along afirst flow pathway along an exterior surface of the impeller, a majorityof the blood flowing along the first flow pathway being directed along alongitudinal axis of the blood flow assist system. In some embodiments,the system includes a second flow pathway through a lumen of theimpeller shaft, the second impeller configured to direct blood from thesecond flow pathway radially outward relative to the longitudinal axis.In some embodiments, an angled cavity extends inwardly and distallyrelative to the generally proximally-facing surface of the flange. Insome embodiments, the drive unit comprises a convex member sized to fitwithin the angled cavity. In some embodiments, the system includes asleeve bearing disposed about the impeller shaft at a location distalthe impeller. In some embodiments, in a cross-section takenperpendicular to an axis of rotation of the impeller, a support surfaceof the sleeve bearing is disposed about only a portion of a perimeter ofthe impeller shaft at a selected axial location, such that, when theimpeller shaft is rotated about the axis of rotation, an exteriorsurface of the impeller shaft at the selected axial location iscyclically exposed to blood during operation of the blood flow assistsystem. In some embodiments, the system includes a pump housing, theimpeller assembly disposed at least partially within the pump housing.In some embodiments, the pump housing includes an outlet, the outletdisposed proximal the impeller. In some embodiments, the second impelleris disposed proximal a distal end of the outlet. In some embodiments,the system includes a support structure coupled to or formed with thepump housing, the support structure comprising struts configured tocontact a blood vessel wall to maintain spacing of the pump housing froma blood vessel wall in which the pump housing is disposed. In someembodiments, the blood flow assist system comprises a percutaneous pumpconfigured for percutaneous insertion to a treatment location within abody of a patient. A motor can be mechanically coupled with the drivemagnet and a power wire connected to the motor, the power wire extendingproximally from the motor.

In several embodiments, a method of operating a blood flow assist systemis disclosed. The method can include or consist essentially ofpercutaneously delivering an impeller assembly to a treatment locationin a blood vessel of a patient, the impeller assembly comprising a rotorassembly and an impeller coupled with the rotor assembly, the rotorassembly comprising a concave bearing surface, the blood flow assistsystem comprising a drive unit proximal the impeller assembly, the driveunit comprising a drive magnet and a drive bearing between the drivemagnet and the impeller assembly, the drive bearing comprising a convexbearing surface fitting within the concave bearing surface, the convexbearing surface comprising a plurality of distally-projecting segments,the plurality of distally-projecting segments spaced apartcircumferentially to define at least one channel between adjacentsegments; pumping blood longitudinally along a length of the impellerassembly and radially outwardly through the at least one channel; andremoving the impeller assembly from the patient. In some embodiments,the method includes directing blood radially outward between the driveunit and a second impeller disposed proximal the impeller, the driveunit having a distal end disposed distal of a proximal end of the secondimpeller. In some embodiments, the method includes providing relativemotion between the impeller assembly and a sheath to cause a pluralityof struts to self-expand radially outwardly to engage a wall of theblood vessel. In some embodiments, providing opposite relative motionbetween the impeller assembly and the sheath to cause the plurality ofstruts to collapse within the sheath. In some embodiments, the rotorassembly comprises an impeller shaft on which the impeller is disposedand a sleeve bearing disposed about the impeller shaft distal theimpeller, the method comprising cyclically exposing an exterior surfaceof the impeller shaft to blood at a selected axial location. In someembodiments, the method includes supplying electrical current to a motorby way of a power wire, the motor being operably connected to theimpeller assembly, the power wire extending outside a body of thepatient.

In several embodiments, a method of manufacturing a blood flow assistsystem is disclosed. In some embodiments, the method includes orconsists essentially of providing an impeller assembly comprising arotor assembly and an impeller coupled with the rotor assembly, therotor assembly comprising a concave bearing surface; and providing adrive unit proximal the impeller assembly, the drive unit comprising adrive magnet and a drive bearing between the drive magnet and theimpeller assembly, the drive bearing comprising a convex bearing surfaceshaped to fit within the concave bearing surface, the convex bearingsurface having a distal end disposed distal of a proximal end of therotor assembly.

In some embodiments, providing the drive unit comprises forming aplurality of distally-projecting segments in the convex bearing surface,the plurality of distally-projecting segments spaced apartcircumferentially to define at least one channel between adjacentsegments. In some embodiments, the method comprises at least partiallydisposing the impeller in a pump housing. In some embodiments, themethod comprises providing a support structure to be coupled to orformed with the pump housing, the support structure comprising strutsconfigured to contact a blood vessel wall to maintain spacing of thepump housing from a blood vessel wall in which the pump housing isdisposed. In some embodiments, the method comprises providing a motorproximal the impeller, the motor configured to impart rotation to theimpeller. In some embodiments, the method comprises connecting the motorto a power wire that extends proximally relative to the motor.

In several embodiments, a blood flow assist system is disclosed. In someembodiments, the blood flow assist system includes or consistsessentially of an impeller assembly comprising an impeller shaft, afirst impeller disposed on the impeller shaft, and a second impellerdisposed on the impeller shaft spaced apart proximally from the firstimpeller along the impeller shaft; and a drive unit configured to impartrotation to the impeller shaft, the drive unit having a distal enddisposed distal a proximal end of the second impeller. In someembodiments, the first impeller is configured to pump blood along afirst flow pathway along an exterior surface of the first impeller, amajority of the blood flowing along the first flow pathway beingdirected along a longitudinal axis of the blood flow assist system. Insome embodiments, the system includes a fairing disposed about theimpeller shaft between the first impeller and the second impeller, thefirst flow pathway disposed along an angled exterior surface of thefairing. In some embodiments, the system includes a second flow pathwaythrough a lumen of the impeller shaft, the second impeller configured todirect blood from the second flow pathway radially outward relative tothe longitudinal axis. In some embodiments, during operation of theblood flow assist system, blood pumped along the second flow pathwayflows between a proximal end portion of the impeller shaft and thedistal end of the drive unit.

In some embodiments, the drive unit comprises a drive magnet and a drivebearing between the drive magnet and the impeller assembly, the drivebearing comprising a convex bearing surface having a plurality ofdistally-projecting segments, the plurality of distally-projectingsegments spaced apart circumferentially to define at least one channelbetween adjacent segments, the secondary flow pathway comprising the atleast one channel. In some embodiments, the system includes a flangeextending non-parallel from a proximal end portion of the impellershaft, the second impeller disposed comprising a plurality of vanes on agenerally proximally-facing surface of the flange. In some embodiments,the system includes an angled cavity extending inwardly and distallyrelative to the generally proximally-facing surface of the flange. Insome embodiments, the drive unit comprises a convex member sized to fitwithin the angled cavity. In some embodiments, the system includes arotor magnet coupled to the impeller shaft, the rotor magnet disposedadjacent a distally-facing surface of the flange. In some embodiments,the system includes a sleeve bearing disposed about the impeller shaftat a location distal the first impeller. In some embodiments, in across-section taken perpendicular to an axis of rotation of the firstimpeller, a support surface of the sleeve bearing is disposed about onlya portion of a perimeter of the impeller shaft at a selected axiallocation, such that, when the impeller shaft is rotated about the axisof rotation, an exterior surface of the impeller shaft at the selectedaxial location is cyclically exposed to blood during operation of theblood flow assist system. In some embodiments, the system includes apump housing, the impeller assembly disposed at least partially withinthe pump housing. In some embodiments, the pump housing includes anoutlet, the outlet disposed proximal the first impeller. In someembodiments, the second impeller is disposed proximal a distal end ofthe outlet. In some embodiments, the system includes a support structurecoupled to or formed with the pump housing, the support structurecomprising struts configured to contact a blood vessel wall to maintainspacing of the pump housing from a blood vessel wall in which the pumphousing is disposed. In some embodiments, the first impeller comprises aplurality of outwardly-extending, axially-aligned blades. In someembodiments, a kit includes the blood flow assist system that comprisesa motor assembly configured to impart rotation to the first impeller andthe second impeller and a power wire electrically connected to the motorassembly. The kit can include a console configured to electricallyconnect to the power wire. In some embodiments, the impeller shaft, thesecond impeller, and the flange form an integrated rotor core, the firstimpeller attached to the impeller shaft. In some embodiments, theimpeller shaft, the first impeller, the second impeller, and the flangeform a unitary body.

In several embodiments, a blood pump is disclosed. In some embodiments,the blood pump includes or consists essentially of a primary impeller, aflow tube routed through the primary impeller, a rotatable piececomprising a secondary impeller, a conical opening, and the flow tube,and a drive unit sealed by a drive unit cover, the drive unit covercomprising a conical member that matches the contour of and fits insidethe conical opening. In some embodiments, the drive unit comprises amagnet sealed in the drive unit cover. In some embodiments, the driveunit comprises a motor, the magnet rotatable by the motor. In someembodiments, the secondary impeller comprises a plurality of vanes.

In several embodiments, a method of operating a blood flow assist systemis disclosed. In some embodiments, the method includes or consistsessentially of percutaneously delivering an impeller assembly to atreatment location in a blood vessel of a patient, the impeller assemblycomprising an impeller shaft, a first impeller disposed on the impellershaft, and a second impeller disposed on the impeller shaft spaced apartproximally from the first impeller along the impeller shaft; pumpingblood along a first flow pathway and a second flow pathway, the firstflow pathway disposed along an exterior surface of the first impeller, amajority of he blood flowing along the first flow pathway being directedalong a longitudinal axis of the blood flow assist system, the secondflow pathway disposed through a lumen of the impeller shaft, the secondimpeller directing blood from the second flow pathway radially outwardrelative to the longitudinal axis; and removing the blood flow assistsystem from the patient. In some embodiments, the method comprisesdirecting blood radially outward between the second impeller and a driveunit, the drive unit having a distal end disposed distal of a proximalend of the second impeller. In some embodiments, the method comprisesproviding relative motion between the impeller assembly and a sheath tocause a plurality of struts to self-expand radially outwardly to engagea wall of the blood vessel. In some embodiments, the method comprisesproviding opposite relative motion between the impeller assembly and thesheath to cause the plurality of struts to collapse within the sheath.In some embodiments, a sleeve bearing is disposed about the impellershaft distal the first impeller, the method comprising cyclicallyexposing an exterior surface of the impeller shaft to blood at aselected axial location. In some embodiments, the method comprisessupplying electrical current to a motor by way of a power wire, themotor being operably connected to the impeller assembly, the power wireextending outside a body of the patient.

In several embodiments, a method of manufacturing a blood flow assistsystem is disclosed. In some embodiments, the method includes orconsists essentially of mounting a first impeller on an impeller shaft,a flange disposed at a proximal end of the impeller shaft; and providinga second impeller spaced apart proximally from the first impeller alongthe impeller shaft, the second impeller disposed on a proximally-facingsurface of the flange. In some embodiments, the method comprises atleast partially disposing the first impeller and the second impeller ina pump housing. In some embodiments, the method comprises providing asupport structure to be coupled to or formed with the pump housing, thesupport structure comprising convex contact pads configured to contact ablood vessel wall to maintain spacing of the pump housing from a bloodvessel wall in which the pump housing is disposed. In some embodiments,the method comprises comprising providing a motor proximal the secondimpeller, the motor configured to impart rotation to the impeller shaft.In some embodiments, the method comprises connecting the motor to apower wire that extends proximally relative to the motor, the motorsized to be inserted into a patient's vasculature and the power wireconfigured to extend through the vasculature to a location outside thepatient's body.

In several embodiments, a blood flow assist system is provided. In someembodiments, the system comprises or consists essentially of an impeller(or first impeller), a lumen extending through the first impeller alonga longitudinal axis of the first impeller, a primary flow pathway alongan exterior surface of the first impeller, and a secondary flow pathwayalong the lumen. In some embodiments, the system includes an impellerassembly comprising an impeller shaft with the impeller disposed on theimpeller shaft, the impeller shaft including the lumen extending from adistal end of the impeller shaft to a proximal end of the impellershaft. In some embodiments, a drive unit configured to impart rotationto the impeller shaft and the impeller is provided, at least a portionof the drive unit positioned proximal the proximal end of the impellershaft. In one embodiment, during operation of the blood flow assistsystem, blood is pumped proximally along the primary flow pathway andthe secondary flow pathway. In some embodiments, the blood flow assistsystem includes a pump housing. In one embodiment, the primary flowpathway is disposed between the exterior surface of the first impellerand the pump housing is also provided. For example, the primary flowpathway can be disposed between (and extend from) a radially outermostsurface of the first impeller to an internal wall of the pump housing.In one embodiment, during operation of the blood flow assist system,blood pumped along the secondary flow pathway flows between the proximalend of the impeller shaft and the drive unit. In one embodiment, thedrive unit comprises a drive magnet and a drive bearing between thedrive magnet and the impeller assembly, the drive bearing comprising aconvex bearing surface having a plurality of distally-projectingsegments, the plurality of distally-projecting segments spaced apartcircumferentially to define at least one channel between adjacentsegments, the secondary flow pathway comprising the at least onechannel. In some embodiments, a second impeller is disposed on theimpeller shaft spaced apart proximally from the first impeller along theimpeller shaft. The blood flow assist system can include a flange at aproximal end of the impeller shaft, the second impeller disposed on aproximally-facing surface of the flange. In some embodiments, theimpeller shaft, the second impeller, and the flange form an integratedrotor core, the first impeller attached to the impeller shaft. In someembodiments, the impeller shaft, the first impeller, the secondimpeller, and the flange form a unitary body. In some embodiments,during operation of the blood flow assist system, blood pumped along thesecondary flow pathway flows between a proximal end of the impellershaft and the drive unit. In some embodiments, a kit can include theblood flow assist system that further includes a motor assemblyconfigured to impart rotation to the impeller and a power wireelectrically connected to the motor assembly. The kit can include aconsole configured to electrically connect to the power wire.

In several embodiments, a blood flow assist system is disclosed. In someembodiments, the blood flow assist system includes or consistsessentially of a pump housing; an impeller assembly disposed in the pumphousing, the impeller assembly comprising an impeller shaft and animpeller on the impeller shaft, the impeller shaft configured to rotateabout an axis of rotation; and a sleeve bearing disposed about theimpeller shaft distal the impeller. In some embodiments, the sleevebearing has an inner support structure supporting the impeller shaft, anouter support structure coupled to or formed with the pump housing, anda connecting structure extending radially between the inner supportstructure and the outer support structure. In some embodiments, theinner support structure comprises a distal boundary, the distal boundaryangled relative to the axis of rotation such that, in a cross-sectiontaken perpendicular to the axis of rotation, only a portion of thedistal boundary is disposed about the impeller shaft at a selected axiallocation along the axis of rotation, such that, when the impeller shaftis rotated about the axis of rotation, an exterior surface of theimpeller shaft at the selected axial location is cyclically exposed toblood during operation of the blood flow assist system. In someembodiments, in a cross-section taken perpendicular to the axis ofrotation, a support surface of the sleeve bearing is disposed about onlya portion of a perimeter of the impeller shaft at a selected axiallocation along the axis of rotation, such that, when the impeller shaftis rotated about the axis of rotation, an exterior surface of theimpeller shaft at the selected axial location is cyclically exposed toblood during operation of the blood flow assist system. In someembodiments, at all axial locations along the axis of rotation along alength of the sleeve bearing, the support surface of the sleeve bearingis disposed only partially about the perimeter of the impeller shaft. Insome embodiments, at an axial location along the axis of rotation, asupport surface of the sleeve bearing is disposed only partially about aperimeter of the impeller shaft. In some embodiments, the systemincludes a drive unit configured to impart rotation to the impellershaft, wherein the drive unit comprises a drive magnet and a drivebearing between the drive magnet and the impeller assembly, the drivebearing comprising a convex bearing surface and a plurality ofdistally-projecting segments extending from the convex bearing surface,the plurality of distally-projecting segments spaced apartcircumferentially to define at least one channel between adjacentsegments.

In some embodiments, the support surface comprises a crenulated surfaceas shown in a side view of the sleeve bearing. In some embodiments, thesupport surface is disposed completely about the perimeter of theimpeller shaft at a second axial location along the axis of rotation. Insome embodiments, the system includes a pump housing, the impellerassembly disposed in the pump housing. In some embodiments, the systemincludes a support structure coupled with the pump housing, the supportstructure comprising struts configured to contact a blood vessel wall tomaintain spacing of the pump housing from a blood vessel wall in whichthe pump housing is disposed. In some embodiments, the impeller isconfigured to pump blood along a first flow pathway along an exteriorsurface of the impeller, a majority of the blood flowing along the firstflow pathway being directed along the axis of rotation. In someembodiments, the system includes a second impeller disposed on theimpeller shaft spaced apart proximally from the impeller along theimpeller shaft, the second impeller configured to direct blood radiallyoutward relative to the axis of rotation from a second flow pathway in alumen of the impeller shaft. In some embodiments, the system includes aflange extending non-parallel from a proximal end portion of theimpeller shaft, the second impeller disposed on a generallyproximally-facing surface of the flange. In some embodiments, a kitincludes the blood flow assist system that comprises a motor assemblyconfigured to impart rotation to the impeller and a power wireelectrically connected to the motor assembly. The kit can include aconsole configured to electrically connect to the power wire.

In several embodiments, a blood pump is disclosed. In some embodiments,the blood pump includes or consists essentially of a pump rotorcomprising a primary impeller and a rotating member including a flowtube that rotates the primary impeller about an axis of rotation; and asleeve bearing that fits around the pump rotor, the sleeve bearingcomprising a bearing interface edge non-perpendicular to the axis ofrotation. In some embodiments, the bearing interface edge comprises anon-circular sleeve edge that ensures that there are no points on therotating member that remain aligned with the sleeve edge throughoutrotation of the rotating member. In some embodiments, the sleeve bearingexposes at least one point on the rotating member throughout an entireheight of the sleeve bearing so that a surface of the rotating member isonly covered by the sleeve bearing for a portion of rotation. In someembodiments, the bearing interface edge comprises an ellipse. In someembodiments, the bearing interface edge varies in a sinusoidal manner.

In several embodiments, a method of operating a blood flow assist systemis disclosed. In some embodiments, the method includes or consistsessentially of percutaneously delivering an impeller assembly to atreatment location in a blood vessel of a patient, the impeller assemblydisposed in the pump housing, the impeller assembly comprising animpeller shaft and an impeller on the impeller shaft, the impeller shaftconfigured to rotate about an axis of rotation, a sleeve bearingdisposed about the impeller shaft; pumping blood through the blood flowassist system such that an exterior surface of the impeller shaft iscyclically exposed to blood at a selected axial location; and removingthe impeller assembly from the patient. In some embodiments, at theselected axial location along the axis of rotation, a support surface ofthe sleeve bearing is disposed only partially about a perimeter of theimpeller shaft. In some embodiments, the method includes directing bloodlongitudinally along a length of the impeller assembly and radiallyoutwardly between a drive unit and a second impeller disposed proximalthe impeller, the drive unit having a distal end disposed distal of aproximal end of the second impeller. In some embodiments, the methodincludes retracting a sheath to cause a plurality of struts toself-expand radially outwardly to engage a wall of the blood vessel.

In several embodiments, a method of manufacturing a blood flow assistsystem is disclosed. In some embodiments, the method includes orconsists essentially of disposing an impeller assembly disposed in apump housing, the impeller assembly comprising an impeller shaft and animpeller on the impeller shaft, the impeller shaft configured to rotateabout an axis of rotation; and disposing a sleeve bearing about theimpeller shaft, wherein, at an axial location along the axis ofrotation, a support surface of the sleeve bearing is disposed onlypartially about a perimeter of the impeller shaft. In some embodiments,the method includes providing a drive unit proximal the impellerassembly, the drive unit comprising a drive magnet and a drive bearingbetween the drive magnet and the impeller assembly, the drive bearingcomprising a convex bearing surface shaped to fit within the concavebearing surface. In some embodiments, providing the drive unit comprisesforming a plurality of distally-projecting segments in the convexbearing surface, the plurality of distally-projecting segments spacedapart circumferentially to define at least one channel between adjacentsegments. In some embodiments, the method includes providing a supportstructure to be coupled to or formed with the pump housing, the supportstructure comprising struts configured to contact a blood vessel wall tomaintain spacing of the pump housing from a blood vessel wall in whichthe pump housing is disposed. In some embodiments, the method includesproviding a motor proximal the impeller, the motor configured to impartrotation to the impeller. In some embodiments, the method includesconnecting the motor to a power wire that extends proximally relative tothe motor.

In several embodiments, a blood flow assist system is disclosed. Thesystem can include or consist essentially of an impeller assemblycomprising an impeller shaft, an impeller on the impeller shaft, aprimary flow pathway disposed along an exterior surface of the impeller,a rotor assembly at a proximal portion of the impeller shaft, the rotorassembly comprising a concave bearing surface, a flange disposed aboutthe concave bearing surface, a rotor magnet supported by the impellershaft, and a second impeller disposed on a proximally-facing surface ofthe flange, wherein a secondary flow pathway is disposed along a lumenof the impeller shaft, and wherein, during operation of the blood flowassist system, blood is pumped proximally along the primary flow pathwayand the secondary flow pathway; a sleeve bearing distal the impeller,the sleeve bearing disposed about the impeller shaft such that, duringrotation of the impeller shaft, an exterior surface of the impellershaft at a selected axial location is cyclically exposed to blood duringoperation of the blood flow assist system; and a drive unit having adistal end disposed distal a proximal end of the second impeller, thedrive unit comprising a drive magnet and a drive bearing between thedrive magnet and the impeller assembly, the drive bearing comprising aconvex bearing surface shaped to fit within the concave bearing surfaceand a plurality of distally-projecting segments, the plurality ofdistally-projecting segments spaced apart circumferentially to define atleast one channel between adjacent segments, wherein the drive unit isconfigured to cause the drive magnet to impart rotation to the rotormagnet and the impeller shaft. In some embodiments, a kit includes theblood flow assist system that comprises a motor assembly configured toimpart rotation to the impeller and a power wire electrically connectedto the motor assembly. The kit can include a console configured toelectrically connect to the power wire. In some embodiments, the bloodflow assist system comprises a percutaneous pump configured forpercutaneous insertion to a treatment location within a body of apatient.

In several embodiments, a blood flow assist system is disclosed. In someembodiments, the blood flow assist system includes or consistsessentially of a pump configured for percutaneous insertion to atreatment location of a patient; an elongate body extending proximallyfrom the pump; and a retrieval feature between a proximal curved portionof the pump and the elongate body, the retrieval feature comprising anenlarged diameter section and a neck between the enlarged diametersection and the proximal curved portion of the pump. In someembodiments, the enlarged diameter section comprises a first curvedportion having a first radius of curvature and a second curved portionhaving a second radius of curvature different from the first radius ofcurvature. In some embodiments, a first plane extending parallel to alongitudinal axis of the blood flow assist system and intersecting thefirst curved portion defines a first angle between the proximal curvedportion and the first curved portion, and a second plane extendingparallel to the longitudinal axis and intersecting the second curvedportion defines a second angle between the proximal curved portion andthe second curved portion, the second angle different from the firstangle. In some embodiments, the enlarged diameter section comprises aplurality of lobes extending radially outward. In some embodiments, thepump comprises a pump head and a motor housing coupled with the pumphead, a proximal end portion of the motor housing comprising theproximal curved portion. In some embodiments, the pump head comprises apump housing and an impeller in the pump housing, and wherein the motorhousing includes a motor operably coupled with the impeller. In someembodiments, the neck comprises a first depth at a first circumferentialposition of the retrieval feature and a second depth less than the firstdepth at a second circumferential position of the retrieval featurespaced apart from the first circumferential position.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages are described belowwith reference to the drawings, which are intended for illustrativepurposes and should in no way be interpreted as limiting the scope ofthe embodiments. Furthermore, various features of different disclosedembodiments can be combined to form additional embodiments, which arepart of this disclosure. In the drawings, like reference charactersdenote corresponding features consistently throughout similarembodiments. The following is a brief description of each of thedrawings.

FIG. 1A is a schematic perspective, partially-exploded view of a bloodflow assist system, according to various embodiments.

FIG. 1B is a schematic perspective view of a pump at a distal portion ofthe blood flow assist system of FIG. 1A.

FIG. 1C is a schematic perspective, partially-exploded view of the pumpof FIG. 1B.

FIG. 1D is a schematic side view of the pump disposed in a collapsedconfiguration in a delivery sheath.

FIG. 1E is a schematic perspective view of a retrieval feature used toremove the pump, according to some embodiments.

FIG. 2A is a schematic perspective view of a modified sleeve bearingdisposed about an impeller shaft distal an impeller of an impellerassembly.

FIG. 2B is a schematic front plan view of the sleeve bearing of FIG. 2A.

FIG. 2C is a schematic side perspective view of the sleeve bearing ofFIG. 2B.

FIG. 2D is a schematic front plan view of the sleeve bearing andimpeller assembly of FIG. 2A.

FIG. 2E is a schematic side sectional view of the impeller assembly andsleeve bearing of FIG. 2D.

FIG. 2F is a schematic side sectional view of a non-overlapping sleeveassembly, according to another embodiment.

FIG. 2G is a schematic perspective view of a sleeve bearing having acrenulated pattern.

FIG. 2H is a schematic plan view of a sinusoidal pattern of the sleevebearing of FIG. 2G.

FIG. 3A is a schematic perspective view of a drive bearing according tovarious embodiments.

FIG. 3B is a front end view of the drive bearing of FIG. 3A.

FIG. 3C is a side view of the drive bearing of FIG. 3A.

FIG. 3D is a schematic front end view of a drive bearing according toanother embodiment.

FIG. 3E is a schematic front end view of a drive bearing according toanother embodiment.

FIG. 4A is a schematic perspective view of an integrated rotor corecomprising an impeller shaft with flow tube and a secondary impeller.

FIG. 4B is a schematic perspective view of a proximal portion of theintegrated rotor core of FIG. 4A.

FIG. 4C is a sectional view taken along the longitudinal axis of therotor core of FIG. 4B.

FIG. 4D is a schematic proximal end view of the integrated rotor core ofFIG. 4C.

FIG. 5A is a schematic perspective, exploded view of a segmented conebearing comprising a proximal portion of the integrated rotor core andthe drive bearing.

FIG. 5B is a distal end sectional view of the secondary impeller anddrive bearing.

FIG. 6 is a schematic, perspective exploded view of a blood flow assistsystem according to various embodiments.

FIG. 7 is a schematic side sectional view of a pump according to variousembodiments.

FIG. 8A is a schematic side sectional view of a motor housing accordingto various embodiments.

FIG. 8B is a schematic perspective view of a motor and a motor mountsupport.

FIG. 8C is a schematic perspective view of a distal end of a power wireconfigured to supply power to the motor.

FIG. 8D is a schematic perspective view of a proximal end portion of thepower wire.

FIGS. 9A and 9B are schematic side sectional views of primary andsecondary flow pathways through a pump according to various embodiments.

DETAILED DESCRIPTION

Refer now to the drawings wherein depicted elements are not necessarilyshown to scale and wherein like or similar elements are designated bythe same reference numeral through the several views. Referring to thedrawings in general, it will be understood that the illustrations arefor the purpose of describing particular implementations of thedisclosure and are not intended to be limiting thereto. While most ofthe terms used herein will be recognizable to those of ordinary skill inthe art, it should be understood that when not explicitly defined, termsshould be interpreted as adopting a meaning presently accepted by thoseof ordinary skill in the art.

I. Overview of Blood Flow Assist Systems

Various embodiments disclosed herein relate to a blood flow assistsystem 1 configured to provide circulatory support to a patient, asillustrated in FIGS. 1A-1D. The system 1 can be sized for intravasculardelivery to a treatment location within the circulatory system of thepatient, e.g., to a location within the descending aorta of the patient.As shown in FIG. 1A, the system 1 can have a proximal end 21 with aconnector 23 configured to connect to an external control system, e.g.,a console (not shown). The connector 23 can provide electricalcommunication between the control system and a power wire 20 extendingdistally along a longitudinal axis L from the connector 23 and theproximal end 21. The power wire 20 can comprise an elongate body thatelectrically and mechanically connects to a pump 2 at or near a distalend 22 of the blood flow assist system 1, with the distal end 22 spacedapart from the proximal end 21 along the longitudinal axis L.

The pump 2 can comprise a pump head 50 including a pump housing 35connected to a drive unit 9 that includes a motor housing 29. Aretrieval feature 48 can be provided at a proximal end portion of thepump 2. In some embodiments, the retrieval feature can be coupled withthe distal end of the power wire 20 between the power wire 20 and themotor housing 29. After a procedure, the clinician can remove the pump 2from the patient by engaging a tool (e.g., a snare, clamp, hook, etc.)with the retrieval feature 48 to pull the pump 2 from the patient. Forexample, the retrieval feature 48 can comprise a neck 49 (e.g., areduced diameter section) at a proximal curved portion 51 c of the motorhousing 29 and an enlarged diameter section disposed proximal the neck49. The enlarged diameter section can comprise a first curved portion 51a and a second curved portion 51 b, as shown in FIG. 1E. The first andsecond curved portions 51 a, 51 b can comprise convex surfaces, e.g.,convex ball portions. The first and second curved portions 51 a, 51 bcan have different radii of curvature. For example, as shown in FIG. 1E,the first curved portion 51 a can have a larger radius of curvature thanthe second curved portion 51 b. The first curved portion 51 a can bedisposed on opposing sides of the retrieval feature 48 in someembodiments. The second curved portion 51 b can be disposed around thefirst curved portion 51 a and can have a radially-outward facing surfaceand a proximally-facing convex surface coupled to the distal end of thepower wire 20. The neck 49 can have a first depth at a firstcircumferential position of the retrieval feature 48 and a second depthless than the first depth at a second circumferential position of theretrieval feature 48 spaced apart from the first circumferentialposition.

Beneficially, as shown in FIG. 1E, one or more first planes P1 extendingparallel to the longitudinal axis L and intersecting the first curvedportion 51 a can have a first angle or taper between the proximal curvedportion 51 c of the motor housing 29 and the first curved portion 51 a.One or more second planes P2 extending parallel to the longitudinal axisL and intersecting the second curved portion 51 b can have a secondangle or taper (which is different from the first angle or taper)between the proximal curved portion 51 c of the motor housing 29 and thesecond curved portion 51 b. The first angle or taper can provide agradual, continuous (generally monotonically decreasing) geometrictransition between the proximal curved portion 51 c of the motor housing29 and the power wire 20, which can provide for smooth blood flow andreduce the risk of thrombosis. The second curved portion 51 b can serveas a lobe that extends radially outward, e.g., radially farther out thanthe first curved portion 51 a. The second curved portion 51 b can beused to engage with a retrieval device or snare to remove the pump 2from the anatomy. Some cross sections through the longitudinal axis ofthe retrieval feature 48 can contain a substantial neck (e.g., a localminimum in the radius of curvature measured along its central axis)while other cross sections through the longitudinal axis of theretrieval feature 48 can contain an insubstantial local minimum or nolocal minimum. In the illustrated embodiment, there are two first curvedportions 51 a that can serve as a dual lobe retrieval feature. In otherembodiments, more or fewer lobes can be provided to enable pumpretrieval while ensuring smooth flow transitions between the motorhousing 29 and power wire 20.

As shown in FIGS. 1B-1C and 1E, the neck 49 can be disposed between thecurved portions 51 a, 51 b and the proximally-facing convex surface 51 cof the motor housing 29. In the illustrated embodiment, the retrievalfeature 48 can be coupled to or integrally formed with the motor housing29. In other arrangements, the retrieval feature 48 can be disposed atother locations of the pump 2. As shown, the retrieval feature 48 can besymmetrical and continuously disposed about the longitudinal axis L. Inother arrangements, the retrieval feature 48 can comprise a plurality ofdiscrete surfaces spaced apart circumferentially and/or longitudinally.

In the illustrated embodiments, the motor housing 29 (and motor) can bepart of the pump 2 and disposed inside the vasculature of the patient inuse. In other embodiments, however, the motor housing 29 (and motor) canbe disposed outside the patient and a drive cable can connect to theimpeller 6.

As shown in FIGS. 1A-1C, the drive unit 9 can be configured to impartrotation to an impeller assembly 4 disposed in the pump housing 35 ofthe pump head 50. As explained herein, the drive unit 9 can include adrive magnet 17 and a motor 30 (see FIGS. 6-8A) disposed in the motorhousing 29 capped by a distal drive unit cover 11. The drive unit cover11 can be formed with or coupled to a drive bearing 18. The drive magnet17 can magnetically couple with a corresponding driven or rotor magnet12 (see FIG. 7) of the impeller assembly 4 that is disposed within theshroud 16 proximal the impeller 6. The power wire 20 can extend from thetreatment location to outside the body of the patient, and can provideelectrical power (e.g., electrical current) and/or control to the motor30. Accordingly, no spinning drive shaft extends outside the body of thepatient in some embodiments. As explained herein, the power wire 20 canenergize the motor 12, which can cause the drive magnet 17 to rotateabout the longitudinal axis L, which can serve as or be aligned with orcorrespond to an axis of rotation. Rotation of the drive magnet 17 canimpart rotation of the rotor magnet 12 and a primary or first impeller 6of the impeller assembly 4 about the longitudinal axis L. For example,as explained herein, the rotor magnet 12 can cause an impeller shaft 5(which can serve as a flow tube) to rotate which, in turn, can cause thefirst impeller 6 to rotate to pump blood. In other embodiments, thedrive unit 9 can comprise a stator or other stationary magnetic device.The stator or other magnetic device can be energized, e.g., withalternating current, to impart rotation to the rotor magnet 12. In theillustrated embodiments, the impeller 6 can have one or a plurality ofblades 40 extending radially outward along a radial axis R that isradially transverse to the longitudinal axis L. For example, the firstimpeller 6 can have a plurality of (e.g., two) axially-aligned blades 40that extend radially outwardly from a common hub and that have a commonlength along the longitudinal axis L. The curvature and/or overallprofile can be selected so as to improve flow rate and reduce shearstresses. Skilled artisans would appreciate that other designs for thefirst impeller 5 may be suitable.

As shown in FIGS. 1A-1C, the impeller assembly 4 can be disposed in ashroud 16. The impeller shaft 5 can be supported at a distal end by asleeve bearing 15 connected to a distal portion of the shroud 16. Asupport structure such as a localization system can comprise a baseportion 36 coupled with the sleeve bearing 15 and/or the shroud 16. Insome embodiments, the base portion 36, the sleeve bearing 15, and/or theshroud 16 can be welded together. The base portion 36 of the supportstructure or localization system, the sleeve bearing 15, and the shroud16 can cooperate to at least partially define the pump housing 35, asshown in FIGS. 1A and 1C. The localization system can comprise aplurality of self-expanding struts 19 having convex contact pads 24configured to contact a blood vessel wall to maintain spacing of thepump housing 35 from the blood vessel wall in which the pump housing 35is disposed. In FIGS. 1A-1C, the struts 19 of the localization systemare illustrated in an expanded, deployed configuration, in which thecontact pads 24 extend radially outward to a position in which thecontact pads 24 would contact a blood vessel wall within which the pump2 is disposed to at least partially control position and/or orientationof, e.g., to anchor, the pump 2 during operation of the system 1.

A first fluid port 27 can be provided distal the impeller assembly 4 ata distal end of the pump housing 35. The shroud 16 can comprise aproximal ring 26 coupled with the motor housing 29 and a plurality ofsecond fluid ports 25 formed in a proximal portion of the shroud 16adjacent (e.g., immediately distal) the proximal ring 26. As shown inFIG. 1C, the second fluid ports 25 can comprise openings formed betweenaxially-extending members 60 that extend along the longitudinal axis Lbetween the proximal ring 26 and a cylindrical section 59 of the shroud16. In some embodiments, the axially-extending members 60 (also referredto as pillars) can be shaped to serve as vanes that can shape or directthe flow of blood through the second fluid ports 25. For example, invarious embodiments, the axially-extending members 60 can be angled orcurved to match the profile of the impeller blades 40. In otherembodiments, the axially-extending members 60 may not be angled to matchthe blades 40. In some embodiments, the first fluid port 27 can comprisean inlet port into which blood flows. In such embodiments, the impellerassembly 4 can draw blood into the first fluid port 27 and can expel theblood out of the pump 2 through the second fluid ports 25, which canserve as outlet ports. In other embodiments, however, the direction ofblood flow may be reversed, in which case the second fluid ports 25 mayserve as fluid inlets and the first fluid port 27 may serve as a fluidoutlet.

Beneficially, the blood flow assist system 1 can be deliveredpercutaneously to a treatment location in the patient. FIG. 1D shows thepump 2 disposed within an elongate sheath 28. As shown, the struts 19are held in a collapsed configuration by the inner wall of the sheath28. In the collapsed configuration, the struts 19 can be compressed to adiameter or major lateral dimension at one or more locations that isapproximately the same (or slightly smaller than) the diameter of theshroud 16. The patient can be prepared for the procedure in acatheterization lab in a standard fashion, and the femoral artery can beexposed. The sheath 28 (or a dilator structure within the sheath 28) canbe passed over a guidewire and placed into the treatment location, forexample, in the descending aorta. After the sheath 28 is placed, thepump 2 can be advanced into the sheath 28, with the pump 2 disposed inthe mid-thoracic aorta, approximately 4 cm below the take-off of theleft subclavian artery. In other embodiments, the pump 2 and sheath 28can be advanced together to the treatment location. Positioning the pump2 at this location can beneficially enable sufficient cardiac support aswell as increased perfusion of other organs such as the kidneys. Once atthe treatment location, relative motion can be provided between thesheath 28 and the pump head (e.g., the sheath 28 can be retractedrelative to the pump 2, or the pump 2 can be advanced out of the sheath28). The struts 19 of the localization system can self-expand radiallyoutwardly along the radial axis R due to stored strain energy into thedeployed and expanded configuration shown in FIGS. 1A-1C. The convexcontact pads 24 can engage the blood vessel wall to stabilize (e.g.,anchor) the pump 2 in the patient's vascular system. Once anchored atthe treatment location, the clinician can engage the control system toactivate the motor 30 to rotate the impeller assembly 4 to pump blood.

Thus, in some embodiments, the pump 2 can be inserted into the femoralartery and advanced to the desired treatment location in the descendingaorta. In such arrangements, the pump 2 can be positioned such that thedistal end 22 is upstream of the impeller 6, e.g., such that thedistally-located first fluid port 27 is upstream of the second fluidport(s) 25. In embodiments that access the treatment location via thefemoral artery, the first fluid port 27 can serve as the inlet to thepump 2, and the second ports 25 can serve as the outlet(s) of the pump2. In other embodiments, however, the pump 2 can be insertedpercutaneously through the left subclavian artery and advanced to thedesired treatment location in the descending aorta. In sucharrangements, the pump 2 can be positioned such that the distal end 22of the system 1 is downstream of the impeller 6, e.g., such that thedistally-located first fluid port 27 is downstream of the second fluidport(s) 25. In embodiments that access the treatment location throughthe left subclavian artery, the second fluid port(s) 25 can serve as theinlet(s) to the pump 2, and the first port 27 can serve as the outlet ofthe pump 2.

When the treatment procedure is complete, the pump 2 can be removed fromthe patient. Relative motion opposite to that used for deploying thepump 2 can be provided between the sheath 28 and the pump 2 (e.g.,between the sheath 28 and the impeller assembly 4 and pump housing 35)to collapse the struts 19 into the sheath 28 in the collapsedconfiguration. In some embodiments, the pump 2 can be withdrawn from thesheath 28 with the sheath 28 in the patient's body, and the sheath 28can subsequently removed. In other embodiments, the sheath 28 and thepump 2 can be removed together from the patient's body.

II. Modified Sleeve Bearings

As explained above, in some embodiments the sleeve bearing 15 cansupport a distal end portion 5A of the impeller shaft 5, which cansupport the first impeller 6 and can also serve as a flow tube. Designsmay be generally described from a perspective in which the central axisof rotation of the impeller assembly 4 is oriented along thelongitudinal axis L of the system 1, e.g., vertically for purposes ofdiscussion in some instances. As used herein, proximal and distal ends(or end portions) of a component may be axially spaced apart along thelongitudinal axis L of the system 1. Thus, the sleeve bearing 15 may bedescribed interchangeably in terms of an associated length or height,which extend along the longitudinal axis L. Generally, a rotating member(a shaft or tube such as the impeller shaft 5 shown and describedherein) rotating inside a tubular sleeve or bearing has a bearingsurface that is cylindrically shaped as an open right circular cylinder.This standard bearing design has circular proximal and distal edges(e.g., upper and lower interface edges) that are perpendicular to thelongitudinal axis L of the rotating member or axis of rotation, and acylindrical bearing surface between the edges that remains covered andunexposed by the bearing body. Further, there is a circular set ofpoints where the rotating member (e.g., the shaft 5) and bearinginterface with one another, which may be referred to herein as a bearinginterface or interface edge. In other words, any point on this circle onthe rotating member is always perpendicularly aligned with the edge ofthe sleeve. This condition has been shown to encourage thrombusformation at the sleeve edge(s). This thrombus may grow to form acomplete ring around the sleeve edge, thereby impeding proper operation.

The designs of the modified sleeve bearing 15 described herein have anovel design to reduce or prevent thrombus formation during operation.Turning to FIGS. 2A-2E, one embodiment of such a sleeve bearing 15 isillustrated. The sleeve bearing 15 can comprise an inner supportstructure including an inner sleeve 37 that supports the distal portion5A of the impeller shaft 5. The inner sleeve 37 can be mechanicallycoupled to the first impeller 6 in some embodiments, e.g., by way of athrust ring bearing 14 (see FIG. 6). The thrust bearing 14 can be laserwelded to the inner sleeve 37 in one embodiment. In other embodiments,there may be no thrust bearing 14 between the first impeller 6 and theinner sleeve 37. The sleeve bearing 15 can further include an outersupport structure comprising an outer annular or cylindrical member,sometimes referred to herein as an outer sleeve or outer bearing carrier38 connected to the shroud 16. The outer sleeve or bearing carrier 38can comprise a small radially outer portion of the sleeve bearing 15. Aconnecting structure 39 can extend radially between the inner sleeve 37and the outer bearing carrier 38 to connect the inner sleeve 37 and theouter bearing carrier 38. In variations the connecting structure 39 canbe coupled directly to the shroud 16. The outer bearing carrier 38 canbe eliminated in one embodiment. The outer bearing carrier 38 can beintegrated into or be part of the shroud 16, such that the structure isa monolithic construction and not the assembly of multiple parts. Inother variations the connecting structure 39 can be indirectly coupledto the shroud 16 through a structure other than the annular member orbearing carrier 38.

As explained herein, the pump 2 can have a primary or first flow pathway3A. Blood can flow along the first flow pathway 3A between the outerbearing carrier 38 and the inner sleeve 37 and along an exterior surfaceof the first impeller 6. A majority of the blood flow (e.g., a majorityof the momentum of the total blood flow) through the pump 2 can passalong the primary or first flow pathway 3A. The first flow pathway 3Acan extend radially between the rotating first impeller 6 and thestationary pump housing 35. Accordingly, blood can flow over therotating outermost surface of the first impeller 6 between the firstimpeller 6 and the stationary inner wall of the pump housing 35. Thepump 2 can also have a secondary or second flow pathway 3B along a lumenof the impeller shaft 5, which as explained herein can serve as a flowtube. A minority of the total blood flow can flow along the secondaryflow pathway 3B. For example, in some embodiments, the volume flow ofblood along the secondary flow pathway 3B can be in a range of 0.5% to10% of the volume flow of blood along the primary flow pathway 3A, in arange of 1% to 5% of the volume flow of blood along the primary flowpathway 3A, or in a range of 2% to 3% of the volume flow of blood alongthe primary flow pathway 3A.

As shown in FIGS. 2A, 2C, and 2E, the inner sleeve 37 can have a bearinginterface surface 41 extending between a proximal edge 37B (or “loweredge” if viewed vertically) and a distal edge 37A (or “upper edge” ifviewed vertically) spaced apart from the proximal edge 37B along thelongitudinal axis L. The sleeve bearing 15 can be shaped so that one ormore bearing interface surfaces 41 and/or interface edges (37A, 37B) ofthe inner sleeve 37 are not perpendicular to the axis of rotation orlongitudinal axis L of the sleeve bearing 15. In one embodiment, thebearing interface surface 41 may comprises edges 37A, 37B that formellipse(s) tilted or tapered with respect to the longitudinal axis L ofthe sleeve bearing 15 (FIGS. 2A-2E). In another embodiment, as explainedbelow, the bearing surface(s) 41 may vary in a sinusoidal way to createcrenulated edge(s) (see FIG. 2F). These or other shapes that result innon-circular sleeve edges 37A, 37B ensure that there are no points onthe rotating member or impeller shaft 5 that remain aligned with thesleeve edges 37A, 37B throughout the rotation of the rotating member(e.g., shaft 5), thereby minimizing the potential for thrombusformation. Whereas conventional designs leave an entire right circularcylinder section covered, the modified sleeve bearings 15 expose atleast one point on the rotating member or shaft 5 throughout the entirelength (or height if the sleeve bearing is viewed as being verticallyoriented) of the sleeve bearing 15 so that the rotating member bearinginterface surface 41 is only covered by the sleeve bearing for a portionof rotation. As such, the interfacing bearing surface(s) 41 may havebetter exchange of the lubricating layer of blood than conventionaldesigns.

Thus, in some embodiments, the distal edge 37A can comprise a distalboundary of the inner sleeve 37. The distal boundary (e.g., the distaledge 37A) can be angled relative to the axis of rotation (which isaligned with the longitudinal axis L) such that, in a cross-sectiontaken perpendicular to the axis of rotation L, only a portion of thedistal boundary (e.g., distal edge 37A) is disposed about the impellershaft 5 at a selected axial location along the axis of rotation. In someembodiments, only a portion of a proximal boundary can be disposed aboutthe impeller shaft 5 at a selected axial location along the axis ofrotation. For example, as shown in FIG. 2E, the bearing interfacesurface 41 can have exposed axial regions 42A, 42B comprising axiallocation(s) at which an exterior surface 5′ (see FIG. 2A) of theimpeller shaft 5 is cyclically exposed to blood that flows along thefirst flow pathway 3A. In the exposed axial regions 42A, 42B, thebearing interface surface 41 is disposed about only a portion of aperimeter (e.g., circumference) of the impeller shaft 5. Accordingly,when the impeller shaft 5 is rotated about the axis of rotation (alignedwith the longitudinal axis L), an exterior surface of the impeller shaft5 at a selected axial location within the exposed axial regions 42A, 42Bis cyclically exposed to blood flow in the first pathway 3A duringoperation of the blood flow assist system 1.

In some embodiments, such as that shown in FIGS. 2A-2E, the inner sleeve37 may be partially axially overlapping along the longitudinal axis L.As shown in FIG. 2E, for example, at an example overlappingcross-sectional plane 43, the bearing surface 41 of the inner sleeve 37may be disposed completely around the exterior surface of the impellershaft 5 such that the exterior surface 5′ of the shaft 5 at thatoverlapping cross-sectional plane 43 is not exposed to blood flow in thefirst pathway 3A. For example, in some embodiments, the sleeve bearing15 can have a length along the longitudinal axis L. The inner sleeve 37may be partially overlapping by an amount in a range of 1% to 50% of thelength of the sleeve bearing 15, in a range of 5% to 50% of the lengthof the sleeve bearing 15, in a range of 10% to 50% of the length of thesleeve bearing 15, in a range of 20% to 40% of the length of the sleevebearing 15, or in a range of 25% to 35% of the length of the sleevebearing 15 (e.g., about 30% of the length of the sleeve bearing 15 insome embodiments).

In other embodiments, such as that shown in FIG. 2F, a sleeve bearing15A can comprise an inner sleeve 37 which may be non-overlapping suchthat there are no points on the exterior surface 5′ of the impellershaft 5 that remain covered by the bearing interface surface 41 duringrotation of the impeller shaft 37. In FIG. 2F, all axial locations alongthe length of the inner sleeve 37 comprise an exposed axial region 42,such that the bearing surface 41 of the inner sleeve 37 is disposed onlypartially about the perimeter of the impeller shaft 5 at all axiallocations along the length of the inner sleeve 37. For example, theedge(s) 37A, 37B can comprise non-circular edge(s) that ensures thatthere are no points on the rotating member or shaft 5 that remainaligned with the sleeve edge(s) 37A, 37B throughout an entire rotationof the rotating member or shaft 5. The sleeve bearing 15A can thereforeexpose at least one point on the rotating member or shaft 5 throughoutan entire length (or height) of the sleeve bearing 15A so that theexterior surface 5′ of the shaft 5 is only covered by the inner sleeve37 for a portion of rotation.

Accordingly, in some embodiments the bearing edges 37A, 37B are shapedso that maximum length (or height) of the lower or proximal edge 37B isabove minimum length (or height) of the upper or distal edge 37A in oneor more locations around the circumference of the inner sleeve 37 (FIGS.2E & 3F). In these embodiments, there is at least one point on thebearing interface surface 41 throughout the length (or height) of thebearing interface surface 41 that is exposed and that is not covered bythe inner sleeve 37 of the sleeve bearing 15, 15A. In other words, thesleeve bearing 15, 15A never covers 360° of the rotating member or shaft5 throughout the entire length or height of the bearing interface region41. This interrupted contact of the disclosed embodiments promotesexchange of a lubricating layer blood over the entire bearing interface41 and does not allow blood to stagnate or become trapped.

In some embodiments, the tilt or taper of the sleeve edges 37A, 37B withrespect to the longitudinal axis L (and the axis of rotation) may alsogenerate or enhance fluid dynamic forces that contribute to properbearing operation and reduce contact and wear of the bearing parts. Asone non-limiting example, the fluid near the surface of a particularspot on the rotating member (e.g., shaft 5) may experience increases anddecreases in pressure as it moves under and out from under the innersleeve 37. These pressure changes contribute to lubricating layerformation and dispersal.

The interface between the sleeve bearing 15, 15A and the rotating member(e.g., shaft 5) is lubricated by blood. Depending on geometry, materialsused, and operating conditions, this lubrication may be hydrodynamiclubrication, elastohydrodynamic lubrication, boundary lubrication, ormixed lubrication. The varying exposure of the rotating member surfaceand/or varying edge profile of the sleeve bearing edges 37A, 37B may bedesigned to help encourage a fluid wedge to improve lubrication. As anon-limiting example, viscous drag from a surface patch of the rotatingmember or shaft 5 may increase fluid pressure above that surface patchas it rotates under the sleeve edge(s) 37A, 37B. In some embodiments,the cross-section of the inner bearing surface 41 of the sleeve 37 mayoptionally be made non-circular to aid in wedge pressure generation, forexample by varying the wall thickness of the inner sleeve 37. The sleeveedge profile of the edges 37A, 37B may be beveled or rounded to augmentthis pressure generation.

FIGS. 2G and 2H illustrate another example of a sleeve bearing 15B thathas a non-overlapping design. The sleeve bearing 15B comprises acrenulated bearing in which the bearing interface surface 41 is disposedabout the longitudinal axis L in a repeating, undulating or in somecases a sinusoidal pattern 44. The sinusoidal pattern 44 can havealternately exposed gaps about the perimeter of the impeller shaft 5during rotation such that all axial locations along the length of thesleeve bearing 15B are cyclically exposed to blood flow during operationof the system 1. FIG. 2G shows the inner sleeve 37′ can have anundulating pattern that has a plurality of (e.g., two) distal peaks 61and a plurality of (e.g., two) proximal peaks 62. For example, as shownin FIG. 2G, the peaks 61, 62 can be generally flat with arcuate sections64 extending between the peaks 61, 62. A gap 63 between the arcuatesections 64 can provide for the cyclical exposure of the shaft 5 toblood flow. Thus, during rotation, the shaft 5 can transition fromcovered by the arcuate sections 64 to being uncovered and exposedthrough the gaps 63. In other variations, there can be more than twopeaks in the undulating pattern of the sleeve 37′. FIG. 2H shows aninner sleeve 37″ with another crenulated structure with a sinusoidalpatterns, e.g., with curved peaks 61, 62. In some arrangements, the useof curved peaks 61, 61 (as opposed to sharp or flat peaks) maybeneficially allow for smoother flow profiles.

The rotating member 5 and the sleeve bearings 15, 15A, 15B may each bemade of any suitable blood compatible material. As a non-limitingexample, the rotating member (e.g., the impeller shaft 5) may comprise aflow tube made out a biocompatible polymer, e.g., of PEEK orpolyethylene and/or the sleeve bearing 15, 15A, 15B may be made out of ametal, e.g., titanium or stainless steel. Making the rotating member orshaft 5 as a plastic tube may increase the range over whichelastohydrodynamic lubrication is present. For example, the use ofmaterials that enable elastic deformation of the materials duringoperation can provide an improved pressure profile.

III. Modified Cone Bearings

As shown in FIGS. 1A, 1C and 6, the drive unit 9 can comprise a drivemagnet 17 and a drive bearing 18 between the drive magnet 17 and theimpeller assembly 4. The drive bearing 18 can provide a magneticcoupling and a fluid bearing interface between the drive magnet 17 and arotor assembly 46 that comprises the driven or rotor magnet 12 and anintegrated rotor core 8 that includes the impeller shaft 5 and asecondary impeller 7, as shown in FIG. 6. In various embodiments, thedrive bearing 18 can comprise a segmented cone bearing. Cone bearingscan comprise a convex (e.g., generally conical) shaped member 45 seatedinside a generally concave (e.g., conical) opening 32 or cavity of therotor assembly 46. The concave opening 32 can serve as a concave bearingsurface sized and shaped to mate with the convex member 45. The concaveopening 32 can comprise an angled concave cavity sized to receive theconvex member 45. The drive unit 9 can comprise a convex member sized tofit within the angled cavity of the concave opening 32.

The bearing interface region of this bearing design can be formed by thematching surfaces of the conical or convex member 45 and the conical orconcave opening 32 and the space between them. A cone bearing canprovide both axial and radial confinement. The axial confinement from asingle cone bearing can be in one direction only. Cone bearings withsteep slopes provide relatively more radial confinement, and conebearings with shallower slopes provide relatively more axialconfinement. In some embodiments, the conical shaped member 45 can bemodified to reduce hemolysis and/or clotting. In some embodiments, theconical member 45 can be truncated by a cylinder coaxial to the axis ofthe cone (or axis of rotation) to remove base portions of the cone. Insome embodiments, the conical member 45 can be truncated by a planeperpendicular to the axis of the cone (creating a frustrum or afrustoconical surface). In other embodiments, the conical member 45 canbe truncated by both a cylinder and a cone. In some embodiments, thesurface of the conical opening 32 may be modified in a similar manner inconjunction with the conical member 45 or instead of the conical member45. One or the other or both of the surfaces of the conical member 45and conical opening 32 may also be modified by holes, gaps, channels,grooves, bumps, ridges, and/or projections. Each of the surfaces of theconical member 45 and conical opening 32 may also be formed as part ofother components of the pump with any overall shape.

Given the general possibility of holes, grooves, channels, or gaps ineither the conical member 45 and/or conical opening 32, either of theirsurfaces comprise of a plurality of separate bearing surfaces in theplane of the generally conical shape defining the member 45 or opening32. In such a manner the opening 32 and/or the conical member 45 of thebearing pair may be formed by a plurality of separate surfaces or asegmented surface. The plurality of separate surfaces or the segmentedsurface that make up either the conical member 45 or conical opening 32of the bearing pair may extend from the same component or part, or mayextend from distinct components or parts. Grooves and gaps in either theconical member 45 and/or conical opening 32 may be created by removingmaterial from a single generally conical surface or by using a pluralityof separate surfaces.

In some embodiments of a modified cone bearing, the conical member 45 ofthe bearing pair can comprise a convex bearing surface having asegmented frustoconical shape formed from a plurality ofdistally-extending segments 33 (FIGS. 3A-3D). The distally-extendingsegments 33 can extend distally from the drive unit cover 11. Thesegments 33 can be spaced apart circumferentially to define at least onechannel 34 between adjacent segments 33. Three segments 33 are shown inFIGS. 3A-3D, but any suitable number of segments 33 may be utilized. Asshown, the segments 33 can be separate components arising from a commonpart with gaps or channels 34 between them, but the segments 33 may alsobe separated by shallow or deep grooves. The gaps, grooves or channels34 may follow any path. In the illustrated embodiment, the channel(s) 34extend radially outward from a central recess or hollow 31 (alsoreferred to herein as a void) at a location proximal a proximal endportion 5B of the impeller shaft 5. In some embodiments, the width anddepth of any groove or channel 34 may vary along its path. In someembodiments, two or more channels 34 may join or separate. In certainembodiments, two or more channels 34 may join to form the central hollowarea 31 coaxial with the axis of the conical surfaces and/or with thelongitudinal axis of rotation L. In some embodiments, the conicalopening 32 of the bearing pair can be a continuous (e.g., no gaps,channels, or grooves), generally conical surface. The relative angles ofthe cone bearings (e.g., the segments 33) and spacing between segments33 can be selected to provide a desired flow profile through thechannel(s) 34 described herein. For example, increased spacing betweenthe segments 33 can provide increased flow through the channels 34.Together, the segmented conical member 45 of the drive bearing 18 withchannels 34 between the segments 33 and the continuous conical opening32 can serve as a “segmented cone bearing”.

The channels 34 between the segments 33 allow interrupted contactbetween bearing surfaces similar to the interrupted contact describedabove for the modified sleeve bearing 15, 15A, 15B discussed previously.This interrupted contact provides, without limitation, benefits for thesegmented cone bearing analogous to those it provides to the modifiedsleeve bearing 15, 15A, 15B. For example, in embodiments in which theconical opening 32 is part of the rotating member (e.g., the impellershaft 5), the channels 34 between the segments 33 can ensure that atleast one point throughout the length or height of the conical opening32 on the rotating member 5 is intermittently exposed by the conicalopening 32 and not continuously covered by the bearing pair. This designpromotes exchange of a lubricating layer blood over the entire bearinginterface. The channels 34 also generate pressure changes thatcontribute to lubricating layer formation and dispersal as describedabove for the sleeve bearing 15, 15A, 15B.

In some embodiments, additional features may promote blood flow throughthe central hollow 31 and channels 34 of the segmented cone bearing. Insome embodiments blood may flow in through the channels 34 and exit viathe central hollow 31. In other embodiments blood may flow into thecentral hollow 31 (e.g., from the secondary flow pathway 3B of theimpeller shaft 5) and exit via the channels 34. This net flow of bloodthrough the central hollow 31 and channels 34 may serve to ensure thevolume of blood in the channels 34 and central hollow 31 is constantlyflowing to provide a source of fresh blood for lubricating layerexchange, to carry away heat, and/or to reduce the time that blood isexposed to conditions within the bearing region that may increase thepotential for hemolysis or thrombus formation. Accordingly, in variousembodiments, a concave bearing surface (which can comprise or be definedby the concave opening 32) can include a fluid port to deliver bloodproximally along the second flow pathway 3B. The convex bearing surface(which can comprise the convex member 45) can including a void (e.g.,the central hollow 31), which can be disposed on the longitudinal axisL. The one or more channels 34 can extend radially outward from the voidor central hollow 31. The void can be in fluid communication with thefluid port (e.g., an interface between the flow tube 5 and the conicalopening 32) so as to direct blood radially outward along at least onechannel 34.

As shown in FIG. 5A, the segments 33 of the convex member 45 can beshaped to fit within the concave bearing surface comprising the concaveopening 32. In some embodiments, as shown in FIGS. 4A-5B, a directsecondary flow pathway 3B (for example through the flow tube of theimpeller shaft 5 shown in FIGS. 4B-4D and 5B) may provideproximally-flowing blood into the central hollow 31. In some embodimentsa secondary or second impeller 7 may be used to drive the secondary flowof blood through the bearing region, e.g., through the second flowpathway 3B, the central hollow 32, and radially outwardly through thechannel(s) 34. The primary impeller 6 of the pump and/or the additionalsecondary impeller 7 may assist in drawing the blood proximally anddirecting the blood radially outwardly along the channel(s) 34. FIGS.4A-4D show the secondary impeller 7 that draws blood out through thechannels 34 of the segmented cone bearing. As explained herein, thesecondary impeller 7 and impeller shaft 5 can form an integrated rotorcore 8. The secondary impeller 7 can have a plurality of vanes 10 asexplained herein to assist in directing blood radially outward throughthe channel(s) 34 of the drive bearing 18.

Keeping the segmented cone bearing elements or segments 33 near thecentral longitudinal axis L of the pump can have several advantages. Forexample, in the illustrated embodiment, the bearing elements 33 can bemore directly exposed to the blood flow from the flow tube of theimpeller shaft 5 along the second flow pathway 3B. Further, the bearingelements 33 can have a smaller radius where the linear speed of therotating member is lower. Placing the bearing elements or segments 33near the axis L of the pump allows the vanes 10 of the secondaryimpeller 7 to be placed at a greater radius where the linear speed ofthe rotating member or shaft 5 is higher.

FIG. 3D shows an embodiment in which the channels 34 between thesegments 33 follow a curved path from the central hollow 31. Thechannels 34 can be configured to increase flow and reduce shear forceson the blood. In some embodiments, the depth of the channels 34 may bevaried to form a central flow diverter 31 a as shown in, e.g., FIG. 3E.The flow diverter 31 a may comprise a distally-extending projection(e.g., a cylindrical projection, a conical projection, a pyramidalprojection, etc.) disposed in a central region of the bearing betweenthe segments 33. In the illustrated embodiment, the flow diverter 31 acan comprise a symmetrical flow diverter. The flow diverter 31 a may aidblood coming from the flow tube or lumen of the shaft 5 to transitionfrom axial flow to radial flow to exit through the channels 34. The flowdiverter may optionally be manufactured as one or more separate piecesthat are then attached in the central hollow 31 and/or channels 34. Insome embodiments, the flow diverter 31 a may comprise a generally rightcylindrical shape extending distally from the bearing 18. In otherembodiments, the flow diverter 31 a can have a tapered, for example,conical, profile.

The interface between the segments 33 of the conical member 45 andconcave, e.g., conical, opening 32 of the segmented cone bearing can belubricated by blood. Depending on geometry, materials used, andoperating conditions, this lubrication may be hydrodynamic lubrication,elastohydrodynamic lubrication, boundary lubrication, or mixedlubrication. The channels 34 between the segments 33 of the conicalmember 45 of the bearing pair may promote fluid exchange so that aportion of the blood that makes up the lubricating layer between aregion of the conical opening 32 of the bearing pair over one segment 33of the conical member of the bearing pair is replaced by fresh blood inthe lubricating layer that forms between that same region of the conicalopening 32 of the bearing pair and the next segment 33 of the conicalmember of the bearing pair during rotation. The width and depth of thechannels 34 can be altered to encourage this exchange. In variousembodiments, the height and lateral spacing of the segments 33 can beselected to provide a desired channel depth and width. For example, awidth of the channels 34 can be in a range of 0.02″ to 0.06″, in a rangeof 0.03″ to 0.05″, or in a range of 0.035″ to 0.045″ (for example, about0.04″ in some embodiments). The surfaces of the segments 33 of conicalmember of the bearing pair along the channels 34 form the leading andtrailing edges (as seen by a region of the conical opening 32 of thebearing pair) of the segments 33 of the conical member of the bearingpair. The distance of the leading and trailing edges from the conicalopening 32 may also be modified to encourage fluid exchange. Forexample, the edges may be beveled or rounded or the distance of theleading and trailing edges may taper away or towards the surface of theconical opening 32.

The surfaces of the segments 33 of the conical member 45 of the bearingpair may also be modified to diverge from a perfect conical surface topromote formation of a lubricating layer. For example, one or moresurfaces of the segments 33 of the conical member 45 of the bearing pairmay be shaped so the normal distance to the surface of the conicalopening 32 of the bearing pair decreases from the leading edge to thetrailing edge. Such a surface contour may encourage creation of fluidwedges between the segments 33 of the conical member 45 and the conicalopening 32 of the bearing pair for improved lubrication. In anotherembodiment, the surfaces of the segments 33 of the conical member 45 andconical opening 32 of the bearing pair may be smooth and well matched toallow a relatively thin lubricating layer of relatively uniformthickness to form. It should be appreciated that although conical member45 and conical opening 32 are described as having a generally conicalshape in some embodiments, the member 45 and opening 32 may generally beconsidered convex member 45 and concave opening 32. The shapes of theconvex member and the concave opening 32 may be any suitable matingshapes.

The flow of blood driven by the secondary impeller 7 from the centralhollow 31 through the channels 34 provides fresh blood for exchange ofthe lubricating layers and carries away heat in the bearing region. Bothfunctions are important to reducing the potential for thrombus formationin the segmented cone bearing.

The segments 33 of the conical member 45 of the bearing pair and theconical opening 32 of the bearing pair may each be made of any suitableblood compatible bearing material. As a non-limiting example, thesegments 33 of the conical member of the bearing pair may be made out oftitanium or stainless steel and/or the conical opening 32 of the bearingpair may be made out of PEEK or polyethylene.

By making one side of the bearing pair relatively hard and the otherside of the bearing pair relatively soft, the bearing pair may initiallyundergo boundary or mixed lubrication where surface asperities are wornto the point where the surfaces of the conical member and conicalopening are smooth and well-matched enough for hydrodynamic orelastohydrodynamic lubrication to dominate. Having one side of thebearing pair be relatively softer may increase the range over whichelastohydrodynamic lubrication is present. In some embodiments, thecontinuous, conical opening 32 of the bearing pair will be softer andthe segmented, conical member of the bearing pair will be harder. Thisarrangement may help preserve special geometric features of the segments33 on the conical member of the bearing pair. In some embodiments, thecontinuous, conical opening 32 of the bearing pair will be harder andthe segmented, conical member 45 of the bearing pair will be softer.This arrangement may help preserve the surface of the opening 32 as asurface of rotation about the longitudinal axis L. In other variationsthe conical opening 32 and the conical member 45 can be of similar oreven the same hardness which can provide the advantage of dimensionaland shape stability throughout the operation of the pump 2.

In cases where hydrodynamic lubrication dominates, the normal distancebetween the segments 33 on the conical member of the bearing pair andthe conical opening 32 of the bearing pair may be small enough toexclude red blood cells. In these cases, exchange of the lubricatinglayer may be less important as long as heat is still transferred away.Given sufficient exclusion of red blood cells, a continuous (e.g.,without channels or grooves) conical member 45 of the bearing pair maystill demonstrate low potential for thrombus formation as long as heatcan be transferred away quickly enough. In some embodiments, this may beaccomplished by eliminating or covering the channels 34 to form acontinuous conical surface. Blood flow through the covered channels 34may transfer sufficient heat from the bearing pair.

The segmented bearing embodiments described above provide an additionaladvantage of enhancing the flexibility of the portion of the pump 2 inthe vicinity of the pump head 50. The impeller assembly 4 can be coupledwith the drive unit 9 in a manner that permits some motion between theimpeller assembly 4 and the cover 11. For example, the pump 2 may bedelivered through tortuous or curving vasculature or may be insertedfrom outside the patient to inside a blood vessel in tight bends. Theimpeller assembly 4 can tip toward one or more of the segments 33 andaway from one or more segments at the conical opening 32 such thatproximal end face of the impeller assembly is at a non-parallel angle tothe distal face of the cover 11. The motion may be significant comparedto a mounting of the impeller assembly 4 on a shaft rotatably supportedin a drive unit. The tipping of the impeller assembly 4 can occur with aflexing of the shroud 16, which may be flexed in high bending stressmaneuvers. In some embodiments, the shroud 16 is made of an elasticmaterial, such as nitinol, such that the pump head 50 can flex andelastically return to an undeflected state without elongation.

IV. Impeller Shaft with Flow Tube Through Primary Impeller

FIGS. 4A-5B and 7 illustrate how the flow tube of the impeller shaft 5may be routed through the primary impeller 6. This allows for a compactpump rotor assembly 46 in which the primary and secondary flow pathways3A, 3B are separate and flow in the same direction through the system 1as shown in FIGS. 9A-9B. Having the two flow paths flow pathways 3A, 3Bin the same direction minimizes or reduces the probability of bloodrecirculating through the pump. In some embodiments, the primaryimpeller 6 may also have a thrust ring 14 or thrust surface designed tolimit axial motion in the upstream or distal direction by contacting acorresponding thrust ring or thrust surface of the sleeve bearing 15.The primary impeller 6 may have the features described in U.S. Pat. Pub.No. 2017/0087288, incorporated by reference herein.

V. Secondary Impeller

As explained herein, the secondary impeller 7 can be disposed proximalthe primary impeller 6. In some embodiments, as shown in FIGS. 4A-7, thesecondary impeller 7 can comprise a flange 47 extending non-parallel(e.g., radially outward along the radial axis R) from the proximal endportion 5B of the impeller shaft 5 and a plurality of vanes 10 on aproximally-facing surface of the flange 47. The flange 47 can extendnon-parallel and radially outward from the impeller shaft 5. In someembodiments, the flange 47 may not extend radially beyond the shroud 16.In some embodiments, the flange 47 may not extend radially beyond anadjacent portion of the impeller assembly 4, e.g., may not extendradially beyond an integrated streamlined fairing 13, discussed below.In some of these embodiments, the flange 47 can comprise a section ofthe combined rotor surface that lies in a plane perpendicular to thelongitudinal axis L. As shown in FIGS. 4A-4C and 5A, the vanes 10 canextend proximally from the flange 47 and can have a curved profilecircumferentially about the longitudinal axis L. The vanes 10 can bedisposed in the space between the proximal face of the flange 47 and thedistal end of the drive unit 9. The concave opening 32 can comprise anangled cavity extending inwardly and distally relative to the generallyproximally-facing surface of the flange 47. The rotor magnet 12 can bedisposed adjacent a distally-facing surface of the flange 47. Each ofthe vanes 10 can have an inner end 10 a disposed at or near the concaveopening 32 and an outer end 10 b extending radially andcircumferentially outward from the inner end 10 a along the flange 47.The flange 47 can be coupled to or formed with the proximal end of theimpeller shaft 5. In some embodiments, for example, the flange 47 can bemonolithically formed with (e.g., seamlessly formed with) the impellershaft 5. In other embodiments, the flange 47 and impeller shaft 5 can beseparate components that are mechanically connected to one another(e.g., welded or otherwise coupled). In some embodiments, the vanes 10can be monolithically formed with the proximally-facing surface of theflange 47. In other embodiments, the vanes 10 can be mechanicallyconnected to the proximally-facing surface of the flange 47.

As shown in FIG. 4D, the vanes 10 can extend circumferentially about thelongitudinal axis L in a manner such that adjacent vanes 10circumferentially overlap. For example, the radially outer end 10 b ofone vane can circumferentially overlap with, and be disposed radiallyoutward from, the radially inner end 10 a of an adjacent vane. The vanes10 can be prevented from contacting the drive unit 9 by the thrustbearing aspect of the segmented cone bearing. As the impeller assembly 4rotates, the vanes 10 can pump blood radially out of the channels 34 inthe segmented cone bearing and thereby increase net flow through theflow tube of the impeller shaft 5 and segmented cone bearing. As shown,blood can exit the flow tube of the impeller shaft 5 at a locationproximal the primary impeller 6 and be driven radially out of thechannels 34 by the vanes 10. In the illustrated embodiment, five (5)vanes 10 are used, but it should be appreciated that fewer than five ormore than five vanes 10 can be used.

As shown in FIGS. 4A, 4C, and 5A, the secondary impeller 7 can have aproximal end 52 at a proximal edge of the vanes 10. Further as shown inFIGS. 3A and 3C, the drive unit 9 can have a distal end 53 at a distalend of the distally-projecting segments 33. As explained above, thedistally projecting convex segments 33 can be received within theconcave opening 32 of the rotor assembly 46. When the convex segments 33are mated within the concave opening 32, the distal end 53 of the driveunit 9 is distal the proximal end 52 of the second impeller 7 (e.g.,distal the proximal-most end of the rotor assembly 46) as shown, forexample, in FIG. 7.

VI. Integrated Rotor Core

As explained herein, in some embodiments the flow tube of the impellershaft 5, the concave opening 32 of the segmented cone bearing, and thesecondary impeller 7 can be integrated into one part as an integratedrotor core 8. Advantages of this approach include, without limitation,simpler assembly (as described below) and minimization or reduction ofjoints between parts (particularly on the inner surface of the flow tubeof the shaft 5). Beneficially, the primary impeller 6 can be disposed on(e.g., mounted on and secured to (e.g., welded to or adhered to)) theimpeller shaft 5, which can provide a compact design.

In various embodiments, therefore, the primary impeller 6 and theimpeller shaft 5 may be separate components, with the impeller 6mechanically connected to the impeller shaft 5. In other embodiments,the primary impeller 6 and impeller shaft 5 can comprise a unitary ormonolithic structure (e.g., a molded or cast structure). Such unitary ormonolithic structures can be formed without seams or joints between thecomponents of the unitary or monolithic structure. Similarly, thesecondary impeller 7 can be disposed on (e.g., mechanically secured to)the proximal end of the impeller shaft 5. In some embodiments, thesecondary impeller 7 can be monolithically formed with the impellershaft 5 so as to form a unitary component (e.g., molded, cast, etc.). Inother embodiments, the secondary impeller 7 and the impeller shaft 5 cancomprise separate components. In some embodiments, the primary impeller6, the secondary impeller 7 (including the flange 47), and the impellershaft 5 can form a unitary or monolithic component or body. In someembodiments, for example, the primary impeller 6, the secondary impeller7, and the impeller shaft 5 can be injection molded over the rotormagnet 12. Where the secondary impeller 5 is molded over the magnet 12,the surface on which the secondary impeller 6 is disposed can beconsidered a flange where the surface extends radially outward from alumen formed in a central portion of the molded part. Beneficially, asexplained above, the integrated rotor core 8 can form a compactstructure. Rotation of the drive magnet 17 can impart rotation to therotor magnet 12, which is also disposed on (e.g., mechanically connectedor mounted on) the impeller shaft 5. Rotation of the rotor magnet 12 canimpart common rotation to the impeller shaft 5, the primary impeller 6,and the secondary impeller 7.

VII. Example Assembled Blood Flow Assist System

FIGS. 7 and 8A-8D show an example schematic view various features of theblood flow assist system 1 described herein. The features describedabove may also be combined in other ways.

As shown in FIGS. 7 and 8A, the system 1 comprises the drive unit 9 withthe motor 30 that can be sealed in the motor housing 29. The drivemagnet 17 can be rotatable by the motor 30 by way of a motor shaft 51.The motor 30 can electrically connect to the power wire 20. As shown inFIGS. 8A and 8C, the power wire 20 can comprise an insulating bodyhaving a central lumen 55 and a plurality of (e.g., three) outer lumens56A-56C extending along a length of the power wire 20. The outer lumens56A-56C can be sized and shaped to receive corresponding electrodes orelectrical wire (not shown) to provide electrical power to the motor 30.For example, the lumens 56A-56C can receive, respectively, a hotelectrode or wire, a neutral electrode or wire, and a ground electrodeor wire. The electrodes can extend through corresponding openings57A-57C of a motor mounting support 54 configured to support the motor30. The central lumen 55 can be sized and shaped to receive an elongatestiffening member or guidewire (not shown). The stiffening member orguidewire can be inserted into the central lumen 55 to help guide thepump 2 to the treatment location. As shown in FIG. 8D, the connector 23near the proximal end 21 of the system 1 can have electrical contacts58A-58C electrically connected to the electrodes in the correspondingouter lumens 56A-56C. The contacts 58A-58C can comprise rings spacedapart by an insulating material and can be configured to electricallyconnect to corresponding electrical components in the control system orconsole (not shown).

The drive magnet 17 can be sealed within the drive unit 9 by the driveunit cover 11 that may also have features that act as the bearingcomponents (e.g., the distally-projecting segments 33). In someembodiments, the top distal portion of the cover 11 may provide thesegments 33 forming the conical member 45 of the segmented cone bearingas described in this disclosure. The corresponding conical opening 32 ofthis bearing pair can be built into a rotatable piece that comprises thesecondary impeller 7 and flow tube or impeller shaft 5 (together, theintegrated rotor core 8). The convex member 45 matches the contour andfits inside of the concave opening 32 of the rotatable piece. Thechannels 34 in the segmented cone bearing provide fluid passages forblood entering the bearing region through the flow tube 5 and forced outof the bearing region by the secondary impeller 7. A lubricating layerof blood between the bearing surfaces of the integrated rotor core 8 andthe matching surfaces of the cone segments 33 provides lubrication,reduces wear, and eases relative motion of the two components. Dependingon the geometry, rotational speed, and materials making up theinterface, this may be hydrodynamic, elastohydrodynamic, boundary, ormixed lubrication.

The rotor magnet 12 of the rotor assembly 46 can be positioned on theintegrated rotor core 8 to be in close proximity to the drive unit 9,thereby allowing the integrated rotor core 8 to be magnetically coupledto the drive unit 9 and rotated as desired. The first or primaryimpeller 6 with an integrated streamlined fairing 13 can be is placedover the rotor magnet 12 and joined to the integrated rotor core 8 to atleast partially form the pump rotor assembly 46. The three-piececonstruction (integrated rotor core 8, magnet, and primary impeller 6with integrated fairing) can have advantages as discussed previouslyrelated to ease of construction and compact design. In some embodiments,the portion of the primary impeller 6 that interfaces with the flow tube5 may be shaped to function as a thrust pad or to be fit with a separatethrust ring 14 to interface with a matching thrust pad on the sleevebearing 15 that fits around the flow tube 5. The rotor magnet 12 andprimary impeller 6 with the fairing 13 may be secured to the integratedrotor core 8 so that the components rotate together.

Alternatively, the pump rotor could be assembled from more than threepieces. In one alternative embodiment, the primary impeller 6 and thefairing 13 are separate pieces. This can allow the primary impeller 6and the fairing 13 to be made of different materials. Alternatively, therotor magnet 12 may be coated to be suitable for blood contact and maynot be covered by the fairing 13, but rather directly joined to theprimary impeller 6. Such a configuration may allow use of a largerdiameter magnet (with corresponding higher torque coupling) in the samepump rotor diameter than would be possible with a magnet inside afairing.

In another alternative embodiment, a separate ring 14 may be addedaround the flow tube 5 above the primary impeller 6. This separate ringwould then serve as the thrust interface that mates with the thrustsurface of the sleeve bearing. The separate ring could be made of adifferent material than the flow tube 5 or primary impeller 6.

The flow tube of the impeller shaft 5 of the pump rotor can fit inside afixed (non-rotating) sleeve bearing 15 (FIG. 7). As explained above, thesleeve bearing 15 can provide radial confinement of the impellerassembly 4 and the rotor assembly 46. The bearing interface comprisesthe outer surface of the impeller shaft 5 and the inner surface of thesleeve bearing 15. The sleeve bearing 15 can have a modified geometry asexplained above that reduces or minimizes continuous coverage of theouter surface of the impeller shaft 5 and thereby reduces the potentialfor thrombosis. The sleeve bearing 15 may also optionally provide athrust bearing surface that interfaces with the optional thrust bearingsurface of the primary impeller 6 or optional thrust ring 14.

The outer bearing carrier 38 of the sleeve bearing 15 can attach to theshroud 16 that fits around the impeller assembly 4 and is attached tothe drive unit cover 11 of the drive unit 9. The connecting structure 39can include an arm or arms may attach directly to the shroud 16 or mayattach to a ring that is then attached to the shroud 16 to provideimproved rigidity and circularity of the shroud 16.

The shroud 16 can comprise a tube with an inlet end and an outlet end.The shroud 16 can be placed over the various internal components thatmake up the pump rotor (e.g., the impeller assembly 4 and the rotorassembly 46). The outlet end of the shroud 16 can be secured to thedrive unit cover 11 of the drive unit 9. The inlet side of the shroud 16can be open to create an inlet port 27. The front bearing is placedwithin the inlet port of the shroud 16 as described above. The outletside of the shroud 16 has openings 25 in the surface of the shroud(outlet ports) that provide outlets for fluid driven by the primaryimpeller 6 and secondary impeller 7.

While some drawings of the system are shown without struts for clarity,the pump may include struts or any other securing means for securing thepump in the circulatory system, such as illustrated in U.S. Pat. Nos.8,012,079 and 9,572,915 and U.S. Pat. Pub. No. 2017/0087288.

VIII. Operation

As shown in FIGS. 9A and 9B, various embodiments of the pump 2 providetwo flow paths 3A, 3B as explained herein. The first flow pathway 3A(red in FIGS. 9A-9B) is driven by the primary impeller 6, which drawsfluid in through the inlet port 27 of the shroud 16 and directs thefluid out of the outlet ports 25 of the shroud 16. The second flow path3B (yellow in FIG. 9A and blue in FIG. 9B) is driven by the secondaryimpeller 7, which draws fluid through the internal secondary flow path3B, e.g., a lumen or flow tube of the impeller shaft 5. The internalflow path passes through the flow tube of the shaft 5 of the integratedrotor core 8. As the fluid reaches the proximal end 5B of the shaft 5,some of the fluid passes through the channels 34 between the conesegments 33 and a smaller fraction passes between the matching conicalsurfaces of the bearing interfaces (e.g., between the convex member 45and the concave opening or cavity 32). The fluid can be driven radiallyoutward by the vanes 10 of the secondary impeller 7. Notably, flow fromboth flow paths can be directed from the inlet 27 to the outlet 25 inthe illustrated embodiment. In other embodiments, as described herein,the flow of blood can be reversed.

It shall be apparent to one of ordinary skill in the art that fluidflowing through the secondary flow path, particularly the fluid layerbetween the matching cone bearing interface surfaces, acts as alubricating layer between the rotor assembly 46 and the fixed segments33 of the segmented cone bearing. Further, the matching conical surfacesof the segmented cone bearing can provide both axial and radialconfinement of the pump assembly 46.

IX. Advantages

Various embodiments disclosed herein can have a number of uniqueadvantages. Many of these advantages are described herein, but they arenot an exhaustive list. The following are only additional non-limitingexamples of advantages, one or more of which can apply to particularembodiments.

-   -   a. Bearing elements (e.g., the sleeve bearing 15, 15A, 15B        and/or the segmented cone bearing) can have surface area contact        rather than point contact or line contact.    -   b. Secondary flow along the second pathway 3B may be in the same        direction as the primary flow pathway 3A to reduce or to        minimize potential recirculation of blood.    -   c. The flow tube or shaft 5, conical opening 32 of segmented        cone bearing, and the secondary impeller 7 can be beneficially        integrated in an integrated rotor core 8.    -   d. Attractive force of the magnetic coupling utilizes a thrust        bearing in only one direction to support the external rotor; no        thrust bearing may be used to prevent movement of the pump rotor        8 away from the drive unit 9.

Embodiments described herein are included to demonstrate particularaspects of the present disclosure. It should be appreciated by those ofordinary skill in the art that the embodiments described herein merelyrepresent non-limiting embodiments of the disclosure. Those of ordinaryskill in the art should, in light of the present disclosure, appreciatethat many changes can be made in the specific embodiments described,including various combinations of the different elements, components,steps, features, or the like of the embodiments described, and stillobtain a like or similar result without departing from the spirit andscope of the present disclosure. From the foregoing description, one ofordinary skill in the art can easily ascertain the essentialcharacteristics of this disclosure, and without departing from thespirit and scope thereof, can make various changes and modifications toadapt the disclosure to various usages and conditions. The embodimentsdescribed hereinabove are meant to be illustrative only and should notbe taken as limiting of the scope of the disclosure.

Conditional language, such as “can,” “could,” “might,” or “may,” unlessspecifically stated otherwise, or otherwise understood within thecontext as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements, and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements, and/or steps are inany way required for one or more embodiments.

The terms “comprising,” “including,” “having,” and the like aresynonymous and are used inclusively, in an open-ended fashion, and donot exclude additional elements, features, acts, operations, and soforth. Also, the term “or” is used in its inclusive sense (and not inits exclusive sense) so that when used, for example, to connect a listof elements, the term “or” means one, some, or all of the elements inthe list. In addition, the articles “a,” “an,” and “the” as used in thisapplication and the appended claims are to be construed to mean “one ormore” or “at least one” unless specified otherwise.

The ranges disclosed herein also encompass any and all overlap,sub-ranges, and combinations thereof. Language such as “up to,” “atleast,” “greater than,” “less than,” “between,” and the like includesthe number recited. Numbers preceded by a term such as “about” or“approximately” include the recited numbers and should be interpretedbased on the circumstances (e.g., as accurate as reasonably possibleunder the circumstances, for example ±5%, ±10%, ±15%, etc.). Forexample, “about 1” includes “1.” Phrases preceded by a term such as“substantially,” “generally,” and the like include the recited phraseand should be interpreted based on the circumstances (e.g., as much asreasonably possible under the circumstances). For example,“substantially spherical” includes “spherical.” Unless stated otherwise,all measurements are at standard conditions including temperature andpressure.

As used herein, a phrase referring to “at least one of” a list of itemsrefers to any combination of those items, including single members. Asan example, “at least one of: A, B, or C” is intended to cover: A, B, C,A and B, A and C, B and C, and A, B, and C. Conjunctive language such asthe phrase “at least one of X, Y and Z,” unless specifically statedotherwise, is otherwise understood with the context as used in generalto convey that an item, term, etc. may be at least one of X, Y or Z.Thus, such conjunctive language is not generally intended to imply thatcertain embodiments require at least one of X, at least one of Y and atleast one of Z to each be present.

Although certain embodiments and examples have been described herein, itshould be emphasized that many variations and modifications may be madeto the humeral head assembly shown and described in the presentdisclosure, the elements of which are to be understood as beingdifferently combined and/or modified to form still further embodimentsor acceptable examples. All such modifications and variations areintended to be included herein within the scope of this disclosure. Awide variety of designs and approaches are possible. No feature,structure, or step disclosed herein is essential or indispensable.

Some embodiments have been described in connection with the accompanyingdrawings. However, it should be understood that the figures are notdrawn to scale. Distances, angles, etc. are merely illustrative and donot necessarily bear an exact relationship to actual dimensions andlayout of the devices illustrated. Components can be added, removed,and/or rearranged. Further, the disclosure herein of any particularfeature, aspect, method, property, characteristic, quality, attribute,element, or the like in connection with various embodiments can be usedin all other embodiments set forth herein. Additionally, it will berecognized that any methods described herein may be practiced using anydevice suitable for performing the recited steps.

For purposes of this disclosure, certain aspects, advantages, and novelfeatures are described herein. It is to be understood that notnecessarily all such advantages may be achieved in accordance with anyparticular embodiment. Thus, for example, those skilled in the art willrecognize that the disclosure may be embodied or carried out in a mannerthat achieves one advantage or a group of advantages as taught hereinwithout necessarily achieving other advantages as may be taught orsuggested herein.

Moreover, while illustrative embodiments have been described herein, itwill be understood by those skilled in the art that the scope of theinventions extends beyond the specifically disclosed embodiments to anyand all embodiments having equivalent elements, modifications,omissions, combinations or sub-combinations of the specific features andaspects of the embodiments (e.g., of aspects across variousembodiments), adaptations and/or alterations, and uses of the inventionsas would be appreciated by those in the art based on the presentdisclosure. The limitations in the claims are to be interpreted fairlybased on the language employed in the claims and not limited to theexamples described in the present specification or during theprosecution of the application, which examples are to be construed asnon-exclusive. Further, the actions of the disclosed processes andmethods may be modified in any manner, including by reordering actionsand/or inserting additional actions and/or deleting actions. It isintended, therefore, that the specification and examples be consideredas illustrative only, with a true scope and spirit being indicated bythe claims and their full scope of equivalents.

What is claimed is:
 1. A blood flow assist system comprising: a pumphousing; an impeller assembly disposed in the pump housing, the impellerassembly comprising an impeller shaft and an impeller on the impellershaft, the impeller shaft configured to rotate about an axis ofrotation; and a sleeve bearing disposed about the impeller shaft, thesleeve bearing having an inner support structure supporting the impellershaft, an outer support structure coupled to or formed with the pumphousing, and a connecting structure extending radially between the innersupport structure and the outer support structure, wherein, in across-section taken perpendicular to the axis of rotation, a supportsurface of the sleeve bearing is disposed about only a portion of aperimeter of the impeller shaft at a selected axial location along theaxis of rotation, such that, when the impeller shaft is rotated aboutthe axis of rotation, an exterior surface of the impeller shaft at theselected axial location is cyclically exposed to blood during operationof the blood flow assist system, and wherein the inner support structurecomprises a distal boundary angled relative to the axis of rotation. 2.The blood flow assist system of claim 1, further comprising a drive unitconfigured to impart rotation to the impeller shaft, wherein the driveunit comprises a drive magnet and a drive bearing between the drivemagnet and the impeller assembly, the drive bearing comprising a convexbearing surface and a plurality of distally-projecting segmentsextending from the convex bearing surface, the plurality ofdistally-projecting segments spaced apart circumferentially to define atleast one channel between adjacent segments.
 3. A kit comprising: theblood flow assist system of 3, and further comprising: a motor assemblyconfigured to impart rotation to the impeller; and a power wireelectrically connected to the motor assembly; and a console configuredto electrically connect to the power wire.
 4. A blood flow assist systemcomprising: a pump housing; an impeller assembly disposed in the pumphousing, the impeller assembly comprising an impeller shaft and animpeller on the impeller shaft, the impeller shaft configured to rotateabout an axis of rotation; and a sleeve bearing disposed about theimpeller shaft, the sleeve bearing having an inner support structuresupporting the impeller shaft, an outer support structure coupled to orformed with the pump housing, and a connecting structure extendingradially between the inner support structure and the outer supportstructure, wherein, in a cross-section taken perpendicular to the axisof rotation, a support surface of the sleeve bearing is disposed aboutonly a portion of a perimeter of the impeller shaft at a selected axiallocation along the axis of rotation, such that, when the impeller shaftis rotated about the axis of rotation, an exterior surface of theimpeller shaft at the selected axial location is cyclically exposed toblood during operation of the blood flow assist system, and wherein theinner support structure comprises a distal boundary angled relative tothe axis of rotation.
 5. The blood flow assist system of claim 4,wherein at all axial locations along the axis of rotation along a lengthof the sleeve bearing, the support surface of the sleeve bearing isdisposed only partially about the perimeter of the impeller shaft. 6.The blood flow assist system of claim 4, wherein, in a cross-sectiontaken perpendicular to the axis of rotation, only a portion of thedistal boundary is disposed about the impeller shaft at the selectedaxial location, such that, when the impeller shaft is rotated about theaxis of rotation, an exterior surface of the impeller shaft at theselected axial location is cyclically exposed to blood during operationof the blood flow assist system.
 7. The blood flow assist system ofclaim 4, further comprising a drive unit configured to impart rotationto the impeller shaft, wherein the drive unit comprises a drive magnetand a drive bearing between the drive magnet and the impeller assembly,the drive bearing comprising a convex bearing surface and a plurality ofdistally-projecting segments extending from the convex bearing surface,the plurality of distally-projecting segments spaced apartcircumferentially to define at least one channel between adjacentsegments.
 8. A kit comprising: the blood flow assist system of claim 4,and further comprising: a motor assembly configured to impart rotationto the impeller; and a power wire electrically connected to the motorassembly; and a console configured to electrically connect to the powerwire.
 9. A blood flow assist system comprising: an impeller assemblydisposed in a pump housing, the impeller assembly comprising an impellershaft and an impeller on the impeller shaft, the impeller shaftconfigured to rotate about an axis of rotation; and a sleeve bearingdisposed about the impeller shaft, the sleeve bearing having an innersupport structure supporting the impeller shaft, the inner supportstructure comprising a boundary angled relative to the axis of rotation,wherein, at an axial location along the axis of rotation, a supportsurface of the sleeve bearing is disposed only partially about aperimeter of the impeller shaft.
 10. The blood flow assist system ofclaim 9, wherein, when the impeller shaft is rotated about the axis ofrotation, an exterior surface of the impeller shaft at the axiallocation is cyclically exposed to blood during operation of the bloodflow assist system.
 11. The blood flow assist system of claim 9, whereinat all axial locations along the axis of rotation along a length of thesleeve bearing, the support surface of the sleeve bearing is disposedonly partially about the perimeter of the impeller shaft.
 12. The bloodflow assist system of claim 9, wherein the axial location is a firstaxial location, and the support surface is disposed completely about theperimeter of the impeller shaft at a second axial location along theaxis of rotation.
 13. The blood flow assist system of claim 9, whereinthe sleeve bearing comprises an outer support structure coupled to orformed with the pump housing and a connecting structure extendingradially between the inner support structure and the outer supportstructure.
 14. The blood flow assist system of claim 13, wherein theboundary comprises a distal boundary angled such that, in across-section taken perpendicular to the axis of rotation, only aportion of the distal boundary is disposed about the impeller shaft atthe axial location, such that, when the impeller shaft is rotated aboutthe axis of rotation, an exterior surface of the impeller shaft at theaxial location is cyclically exposed to blood during operation of theblood flow assist system.
 15. The blood flow assist system of claim 4,further comprising a support structure coupled with the pump housing,the support structure comprising struts configured to contact a bloodvessel wall to maintain spacing of the pump housing from a blood vesselwall in which the pump housing is disposed.
 16. The blood flow assistsystem of claim 9, wherein the impeller is configured to pump bloodalong a first flow pathway along an exterior surface of the impeller, amajority of the blood flowing along the first flow pathway beingdirected along the axis of rotation.
 17. The blood flow assist system ofclaim 16, further comprising a second impeller disposed on the impellershaft spaced apart proximally from the impeller along the impellershaft, the second impeller configured to direct blood radially outwardrelative to the axis of rotation from a second flow pathway in a lumenof the impeller shaft.
 18. The blood flow assist system of claim 17,further comprising a flange extending non-parallel from a proximal endportion of the impeller shaft, the second impeller disposed on agenerally proximally-facing surface of the flange.
 19. The blood flowassist system of claim 9, further comprising a drive unit configured toimpart rotation to the impeller shaft.
 20. The blood flow assist systemof claim 19, wherein the drive unit comprises a drive magnet and a drivebearing between the drive magnet and the impeller assembly, the drivebearing comprising a convex bearing surface having a plurality ofdistally-projecting segments, the plurality of distally-projectingsegments spaced apart circumferentially to define at least one channelbetween adjacent segments.
 21. A kit comprising: the blood flow assistsystem of claim 9, and further comprising: a motor assembly configuredto impart rotation to the impeller; and a power wire electricallyconnected to the motor assembly; and a console configured toelectrically connect to the power wire.
 22. A blood pump comprising: apump rotor comprising a primary impeller and a rotating member includinga flow tube that rotates with the primary impeller about an axis ofrotation; and a sleeve bearing that fits around the flow tube, thesleeve bearing comprising a non-circular bearing interface edgenon-perpendicular to the axis of rotation, the non-circular bearinginterface edge being tilted with respect to the axis of rotation. 23.The blood pump of claim 22, wherein the bearing interface edge comprisesa non-circular sleeve edge that ensures that there are no points on therotating member that remain aligned with the sleeve edge throughoutrotation of the rotating member.
 24. The blood pump of claim 22, whereinthe sleeve bearing exposes at least one point on the rotating memberthroughout an entire height of the sleeve bearing so that a surface ofthe rotating member is only covered by the sleeve bearing for a portionof rotation.
 25. The blood pump of claim 22, further comprising a pumphousing, the pump rotor disposed in the pump housing.
 26. A blood flowassist system comprising: an impeller assembly disposed in a pumphousing, the impeller assembly comprising an impeller shaft and animpeller on the impeller shaft, the impeller shaft configured to rotateabout an axis of rotation; and a sleeve bearing disposed about theimpeller shaft, wherein, at an axial location along the axis ofrotation, a support surface of the sleeve bearing is disposed onlypartially about a perimeter of the impeller shaft, wherein at all axiallocations along the axis of rotation along a length of the sleevebearing, the support surface of the sleeve bearing is disposed onlypartially about the perimeter of the impeller shaft, and wherein thesupport surface comprises a crenulated surface as shown in a side viewof the sleeve bearing.
 27. The blood pump of claim 25, furthercomprising a support structure coupled with the pump housing, thesupport structure comprising struts configured to contact a blood vesselwall to maintain spacing of the pump housing from the blood vessel wallin which the pump housing is disposed.
 28. A blood pump comprising: apump rotor comprising a primary impeller and a rotating member includinga flow tube that rotates with the primary impeller about an axis ofrotation; and a sleeve bearing that fits around the flow tube, thesleeve bearing comprising a bearing interface edge non-perpendicular tothe axis of rotation, wherein the bearing interface edge varies in asinusoidal manner.
 29. The blood pump of claim 28, further comprising apump housing, the pump rotor disposed in the pump housing, and a supportstructure coupled with the pump housing, the support structurecomprising struts configured to contact a blood vessel wall to maintainspacing of the pump housing from the blood vessel wall in which the pumphousing is disposed.